Cronulla Sharks ironman Paul Gallen is on the verge of becoming the first player in NRL history to reach 50,000 career running metres.

According to NRL.com Stats, he has racked up a phenomenal 49,668 metres in his 304 career matches.

Remarkably, Gallen in 2015 became the first player to 40,000 run metres and nobody else has hit that milestone with second-placed Billy Slater on 39,187 metres. The Melbourne Storm veteran should cross 40,000m this year but would need an unlikely three to five more seasons to get to 50,000.

The next seven players are retired, with Anthony Minichiello (39,013), Corey Parker (38,393) and Petero Civoniceva (36,962) the next best. The next active player after Slater is Gallen's former teammate Chris Heighington with 31,687m, who is suiting up for what is likely to be his last season in the Telstra Premiership with the Newcastle Knights.

So whatever figure the tireless Gallen racks up by the time he eventually retires, will be safe for a very long time.

Prolific North Queensland Cowboys lock Jason Taumalolo has improved on his run metre tally every season since his 2010 debut, but at 20,198 metres after 139 games has roughly 40% of Gallen's career metres while playing almost half as many games and would need to match his stunning 2017 output for another six seasons to catch up to where Gallen is now.

It is generally considered 150 metres in a single game is a big achievement - Gallen has averaged just over 163 metres per match across his entire 304-game career. This includes games where he has been forced off injured and the early part of his career in which he came off the bench and even started at five-eighth at times.

The 25 matches Gallen played in 2017 was an equal-career high but netted easily the biggest metres gained figure of his career with a whopping 4559. At his current rate he should pass the 50km mark in round two. Even a sluggish start to 2018 (by his standards) would mean he comfortably runs his 50,000th metre in round three.

His consistency over a long period earned high praise from his coach, Shane Flanagan.

"I haven't seen anything like him; before and after the (2016) grand final was testament to how he looks after himself," Flanagan told NRL.com.

This period included Gallen skipping that year's Dally M Medal presentation to get himself right for the grand final due to a slipped disc in his back. He also landed himself in hospital the day after the premiership victory as a result of the medication he was taking to treat the issue.

"We don't want to talk about it but he doesn't get a lot of injuries," Flanagan said.

"He does all his prehab and rehab and his training – you just couldn't have a better example for our young blokes coming through.

"He's still as strong as anyone in the gym. He might've slowed down a little bit but he's changed his game slightly and more than competes with those guys in his position.

"When he was coming through he could play positions like five-eighth and on the edge because he had a bit of leg speed.

"The leg speed might be gone but he's still as competitive as ever. As far as competitiveness and preparing for games goes, Gal's number one."

Gallen's 2018 co-captain Wade Graham said while it was one thing to be talented, the hard work and dedication required to put up such numbers over a long period was an example for every player.

"It amazes me how he just keeps going," Graham told NRL.com.

"He's still pulling up trees at training, in the gym, he's still ripping in. He's flying. Something to really hang your hat on at the end of your career is durability and how long you played the game for.

"To be the first player ever to reacy 50,000 metres, it's amazing."