They don’t come any bigger – in reputation at least – than Tom Brady. With his decade and a half of calling the shots for the New England Patriots and four Super Bowl rings decorating his fingers, this is a giant of the sport, a genuine all-time great in an era when claims of greatness are too easily made. This is a 38-year-old who has been there, done that and delivered the decisive pass time after time, a man who deserves to be listened to.

Two weeks ago the quarterback watched Rob Gronkowski, one of his go-to men, carted from the field late on. “The Gronk”, as the Colossus of a tight-end is known, had his legs swept away by Denver’s Darian Stewart. Memories of last December flooded back, when Gronkowski was reduced to tears after suffering a knee injury that threatened his livelihood.

This time he was more fortunate, although he remains on the sidelines – another footballer nursing a wounded knee. This week’s absentee lists across the NFL has 359 players out through injury or suspension; 82 with knee problems, nearly double the next most common complaint. Twenty six are missing through concussion. Here is the issue that has become the talk of the locker room over the last few years. Would you take a hit to the head or a hit to the knee? And has the focus on protecting the head – which has been proved potentially life-threatening – meant the knee is now taking the strain?

Brady was asked after the Denver game whether rules introduced over the last five years in an attempt to limit the number of concussions have led to teams switching tackling tactics, aiming low where they would have once gone high.

“I hate to see it but it’s really the only way for the defence to hit now, so…” he said and then shrugged. “I bet if you asked a lot of the players they would probably say they’d rather you go high than low. When you go low that’s what happens.

“You hate to see one of your guys take hits and I do think they should change some of those rules with defenceless receivers.”

Brady’s is not a lone voice and there are many who will have nodded along with what he said. As Michael Bush of the Chicago Bears put it last year: “If you get hit in the knee, that’s your career.”

Tackling has changed markedly since the 1980s, when wrapping up an opponent was the preferred method. Instead, in the 2000s, it has become about hits, bone-jarring collisions. When the rule changes began in 2010 as the NFL belatedly addressed its serious problem with head injuries and their consequences – introducing restrictions on hits to shoulders and heads – players were quick to point out where that would lead.

“Guys are going to be fearful of being fined so they’re going to start going at the knees,” forecast LaMarr Woodley of the Steelers. “That’s going to be a serious problem, knees being blown out, mess up the way they walk for the rest of their lives.”

For some it is a black and white issue. Take a bad hit in the knee and you know about it, excruciating pain, the operating table and possibly the immediate end to your career. Head injuries come in shades of grey – the latest reports suggest it is not the big hits that necessarily lead to chronic traumatic encephalopathy (CTE) but rather the totting up of blow after blow across the course of a career. They go almost unnoticed by the recipient – these are tough men – and it is not until helmets are hung up that the sometimes lethal effects are realised. According to data gathered between 2000 and 2014, knee problems keep players out for longer than any other injury. Between 2002 and 2012 there were an average of 43 anterior cruciate ligament (ACL) related injuries per season. In 2013 that rose to 65 and stuck at that level in 2014. Concussions, meanwhile, have fallen – from 2012 to 2015 they dropped 35 per cent.

When Gronkowski was taken out low by Cleveland safety TJ Ward last year he tore right anterior cruciate and medial collateral ligaments. It threatened his future and there were plenty who suggested it was caused by rule changes.

Gronkowski is 6ft 5in and Denver were accused two weeks ago of deliberately going low having spent much of the game bouncing off his upper body. Players, as in rugby, are getting bigger, stronger, faster and so more difficult to stop. That is one reason advanced for the rash of knee injuries, another is the shorter pre-season teams now undertake in order to limit the wear and tear on players’ bodies – instead, some claim, it leaves those bodies inadequately prepared for the season once the hits start raining in. Changes in footwear that have led to lightweight shoes designed for speed as well as different turf are also cited as contributory factors.

Others point to the concussion rules, believing it pushes the focus from high to low. The latest change aims to protect offensive players attempting to catch an intercepted ball – they “cannot be hit in the head or neck area”. The only choice is to go low.

NFL 2015 in pictures Show all 48 1 /48 NFL 2015 in pictures NFL 2015 in pictures New Orleans Saints 31 Atlanta Falcons 21 Benjamin Watson had a career-high 127 yards as the Saints beat the Falcons 2015 Getty Images NFL 2015 in pictures San Diego Chargers 20 Pittsburgh Steelers 24 Le'Veon Bell scores a 1-yard touchdown to win the game with time running out 2015 Getty Images NFL 2015 in pictures New York Giants 30 San Francisco 49ers 27 Larry Donnell scored a spectacular game-winning touchdown with only 21 seconds left 2015 Getty Images NFL 2015 in pictures Tennessee Titans 13 Buffalo Bills 14 Bills quarterback Tyrod Taylor threw a touchdown and run in another 2015 Getty Images NFL 2015 in pictures Detroit Lions 17 Arizona Falcons 42 Matthew Stafford was benched and the Lions are still winless 2015 Getty Images NFL 2015 in pictures Atlanta Falcons 25 Washington Redskins 19 Robert Alford returns an interception for a long touchdown NFL 2015 in pictures Philadelphia Eagles 39 New Orleans Saints 17 DeMarco Murray finally delivered for the Eagles with 83 yards and a touchdown 2015 Getty Images NFL 2015 in pictures Tampa Bay Buccaneers 38 Jacksonville Jaguars 31 Dough Martin scores one of his three touchdowns for the Bucs 2015 Getty Images NFL 2015 in pictures Green Bay Packers 24 St Louis Rams 10 Aaron Rodgers threw his first home interception in nearly two years - James Jones ran in a long score 2015 Getty Images NFL 2015 in pictures Oakland Raiders 10 Denver Broncos 16 Cornerback Chris Harris Jr returned a late touchdown 74 yards for a decisive score NFL 2015 in pictures Dallas Cowboys 6 New England Patriots 30 Julian Edelman catches a touchdown as the Pats kept their 100 per cent record 2015 Getty Images NFL 2015 in pictures Cincinatti Bengals 27 Seattle Seahawks 24 Andy Dalton led the Bengals to win from 17 points down 2015 Getty Images NFL 2015 in pictures Baltimore Ravens 30 Cleveland Browns 33 Travis Coons kicks a game-winning field goal in OT NFL 2015 in pictures Kansas City Chiefs 17 Chicago Bears 18 Running back Jamaal Charles seriously hurt his knee during the defeat 2015 Getty Images NFL 2015 in pictures Houston Texans 20 Indianapolis Colts 27 Matt Hasselbeck won again in the absence of star man Andrew Luck on Thursday night 2015 Getty Images NFL 2015 in pictures Week 4 Steelers 20 Ravens 23; Dolphins 14 Jets 27; Bills 10 Giants 24; Bucs 23 Panthers 37; Bears 22 Raiders 20; Bengals 36 Chiefs 21; Falcons 48 Texans 21; Colts 16 Jaguars 13; Redskins 23 Eagles 20; Chargers 30 Browns 27; Broncos 23 Vikings 20; 49ers 3 Packers 17; Cardinals 22 Rams 24; Saints 26 Cowboys 20; Seahawks 13 Lions 10 2015 Getty Images NFL 2015 in pictures Green Bay Packers 38 Kansas City Chiefs 28 Randall Cobb scores one of his three touchdowns for the Packers - quarterback Aaron Rodgers threw five in total 2015 Getty Images NFL 2015 in pictures Detroit Lions 12 Denver Broncos 24 Demaryius Thomas scores a touchdown as the Broncos continued their perfect start to the season; the Lions are still without a win 2015 Getty Images NFL 2015 in pictures Seattle Seahawks 26 Chicago Bears 0 Star tight end Jimmy Graham scored his first touchdown as the Seahawks ended their losing streak for their first win of the season 2015 Getty Images NFL 2015 in pictures Miami Dolphins 14 Buffalo Bills 41 Ryan Tannehill threw three interceptions as the Dolphins lost to their divisional rivals 2015 Getty Images NFL 2015 in pictures Arizona Cardinals 47 San Francisco 49ers 7 Cardinals safety Tyrann Mathieu picked off two of Colin Kaepernick's four interceptions 2015 Getty Images NFL 2015 in pictures Baltimore Ravens 24 Cincinnati Bengals 28 AJ Green caught 10 passes for 227 yards and scored two touchdowns as the Bengals beat the Ravens in a topsy-turvy clash 2015 Getty Images NFL 2015 in pictures New York Giants 32 Washington Redskins 21 Rueben Randle celebrates a touchdown as the Giants beat their long-time rivals in New York on Thursday night 2015 Getty Images NFL 2015 in pictures Carolina Panthers 27 New Orleans Saints 22 Josh Normanintercepted a last-gasp touchdown throw from Luke McCown as the Panthers held on against the Saints 2015 Getty Images NFL 2015 in pictures Cleveland Browns 20 Oakland Raiders 27 Latavius Murray rushed for 139 yards and the Raiders ended an 11-game losing streak on the road 2015 Getty Images NFL 2015 in pictures Dallas Cowboys 28 Atlanta Falcons 39 Devonta Freeman ran for three touchdowns as the Falcons came from behind to beat the Cowboys, who were missing stars Tony Romo and Dez Bryant 2015 Getty Images NFL 2015 in pictures Houston Texans 19 Tampa Bay Buccaneers 9 Ryan Mallett secured the first win of his career 2015 Getty Images NFL 2015 in pictures Minnesota Vikings 31 San Diego Chargers 14 Chad Greenway returned a Philip Rivers interception for a touchdown 2015 Getty Images NFL 2015 in pictures Tennessee Titans 33 Indianapolis Colts 35 Frank Gore scored two rushing touchdowns as the Colts and the Titans played out a thriller 2015 Getty Images NFL 2015 in pictures New England Patriots 51 Jacksonville Jaguars 17 Tom Brady became only the fourth quarterback to throw 400 touchdown passes in a career - he threw two against the Jags 2015 Getty Images NFL 2015 in pictures St Louis Rams 6 Pittsburgh Steelers 12 The Steelers won but will be without quarterback Ben Roethlisberger for at least four weeks because of a serious knee injury 2015 Getty Images NFL 2015 in pictures New York Jets 17 Philadelphia Eagles 24 Darren Sproles returns a punt for an 89-yard touchdown - the 5ft 6in running back also rushed for a touchdown 2015 Getty Images NFL 2015 in pictures New England Patriots 28 Pittsburgh Steelers 21 New England Patriots quarter-back Tom Brady throws a pass Getty Images NFL 2015 in pictures San Francisco 49ers 20 Minnesota Vikings 3 Adrian Peterson returned after a year on the sidelines but the Vikings lost to the 49ers Getty Images NFL 2015 in pictures Atlanta Falcons 26 Philadelphia Eagles 24 Julio Jones had 140 yards and two touchdowns as th Falcons impressed against the Eagles Getty Images NFL 2015 in pictures Dallas Cowboys 27 New York Giants 26 Jasson Witten celebrates a last minute touchdown after the Cowboys drove down the field Getty Images NFL 2015 in pictures St Louis Rams 34 Seattle Seahawks 31 The Rams celebrate after Greg Zuerlein's overtime field goal pushed them past their rivals Getty Images NFL 2015 in pictures Tampa Bay Buccaneers 14 Tennessee Titans 42 No 1 draft pick Jameis Winston was outplayed by No 2 pick Marcus Mariota as the Titans beat the Bucs Getty Images NFL 2015 in pictures Chicago Bears 23 Green Bay Packers 31 Former league MVP Aaron Rodgers three three touchdowns as the Packers beat their divisional rivals Getty Images NFL 2015 in pictures Buffalo Bills 27 Indianapolis Colts 14 The Bills surprised play-off contenders the Colts thanks to a great performance by Tyrod Taylor, who impressed in his first NFL start Getty Images NFL 2015 in pictures Kansas City Chiefs 27 Houston Texans 20 Travis Kelce scored two first quarter touchdowns as the Chiefs held on after a late Houston rally Getty Images NFL 2015 in pictures Washington Redskins 10 Miami Dolphins 17 Jarvis Landry returned a punt for what turned out to be the game-winning score Getty Images NFL 2015 in pictures New York Jets 31 Cleveland Browns 10 Ryan Fitzpatrick threw two touchdowns as the Jets had five takeaways to beat the Browns Getty Images NFL 2015 in pictures Jacksonville Jaguars 9 Carolina Panthers 20 Cam Newton and the Panthers managed just 263 total yards but did enough to beat the Jaguars Getty Images NFL 2015 in pictures Denver Broncos 19 Baltimore Ravens 13 Former Raven Darian Stewart intercepted a Joe Flacco pass with 28 seconds left to seal a Broncos win Getty Images NFL 2015 in pictures Arizona Cardinals 31 New Orleans Saints 19 Carson Palmer threw three touchdowns in his comeback game from a torn ACL Getty Images NFL 2015 in pictures San Diego Chargers 33 Detroit Lions 28 Philip Rivers led the Chargers to 30 straight points for San Diego to comeback against Detroit Getty Images NFL 2015 in pictures Cincinnati Bengals 33 Oakland Raiders 13 Jeremy Hill ran for two touchdowns as the Bengals beat the Raiders Getty Images

“It wouldn’t be surprising to see the NFL attempt to add rule protection for lower body injuries,” said Jene Bramel, a doctor and writer on the NFL for the website footballguys.com. “Hitting a quarterback below the knee in the pocket is a penalty. But narrowing the target area for defenders playing at speed is easier written into the rule book than accomplished on the field.”

For the NFL, who two years ago reached a £477m settlement with up to 4,500 former players after being accused of having misled them on the dangers of head injuries, concussion remains the No 1 concern. It is a live issue. In September a study found 87 out of 91 former NFL players tested had a brain disease linked to concussions received during their careers. This week Bennet Omalu, the forensic pathologist and neuropathologist who first discovered CTE in football players, wrote in The New York Times that all children under 18 should be banned from playing high-impact sports like football. He compared playing them to letting your children drink alcohol or smoke. A film, starring Will Smith as Omalu, documenting the doctor’s campaign opens in the US on Christmas Day.

The data around concussion is conclusive. That around the cause of knee injuries is not. For example, Reggie Bush, the 49ers running back, recently tore his ACL after slipping on the concrete surrounds of the field of play in St Louis. There has also been a spate of ACL injuries suffered in pre-season, few of which have involved contact.

Whatever the rules this is a brutal sport. On the first weekend of November the injury count reached 32, many serious. “Speed and size play a role in injury, but football is much more than a contact sport,” said Bramel. “Some refer to it as a collision sport, but it’s really supervised trauma. The force and location of impacts during the game can cause injuries similar to those seen in car accidents or falls. Part of the allure of football has always been the combination of power and athleticism. With that comes the risk of violent impact.”

Brady’s calls deserve to be considered but the overwhelming priority remains to protect the head. After that the sport has to decide how much it wants to change.