NFL Commissioner Roger Goodell has said that the league thinks "everyone should stand for the national anthem. That's an important part of our policy."

However, he stopped short of saying it is a requirement. Mr Goddell noted: "Our players will state to you publicly they are not doing this in any way to be disrespectful to the flag."

"But they also understand how it's being interpreted," he said.

He was speaking at a press conference in New York and addressing the latest controversy over players kneeling while the national anthem is sung ahead of all games.

Donald Trump took to Twitter once again this morning about the NFL, posting that because the league would "not force" players to stand it was "total disrespect for our great country!"

The President has tweeted about the kneeling protest controversy several times in the past few weeks.

The controversy arose from the president's appearance at a Huntsville, Alabama political rally on 22 September.

Mr Trump had said “Wouldn’t you love to see one of these NFL owners, when somebody disrespects our flag, to say, ‘Get that son of a b**** off the field right now! Out! He’s fired,'" using his now infamous line from his reality television programme The Apprentice.

He was referring to NFL player Colin Kaepernick, who has no clear connection to the special election for US Senate seat or Republican Luther Strange's bid for the seat that Mr Trump was there to support.

Kaepernick, currently a free agent without a team, was the first player to kneel during the national anthem ahead of a game while he played for the San Francisco 49ers nearly 16 months ago.

He said: "I am not going to stand up to show pride in a flag for a country that oppresses black people and people of colour."

His protest stemmed from a slew of police-involved shooting deaths of several young black men and teenagers across the US like Michael Brown in Ferguson, Missouri and Trayvon Martin in Sanford, Florida. It sparked controversy among fans.

American sportspeople kneel in protest Show all 14 1 /14 American sportspeople kneel in protest American sportspeople kneel in protest Terrance Smith #48, Eric Fisher #72, Demetrius Harris #84, and Cameron Erving #75 of the Kansas City Chiefs is seen taking a knee before the game against the Los Angeles Chargers at the StubHub Center on 24 September, 2017 in Carson, California Sean M. Haffey/Getty American sportspeople kneel in protest Members of the Dallas Cowboys link arms and kneel during the National Anthem before the start of the NFL game against the Arizona Cardinals at the University of Phoenix Stadium on 25 September, 2017 in Glendale, Arizona Christian Petersen/Getty American sportspeople kneel in protest Bruce Maxwell of the Oakland Athletics kneels as teammate Mark Canha #20 places his hand on Maxwell's shoulder during the singing of the National Anthem before their MLB American League baseball game against the Seattle Mariners at Oakland-Alameda County Coliseum in Oakland, California on 25 September 2017 Reuters/Stephen Lam American sportspeople kneel in protest Members of the Oakland Unified School District Honor Band kneel as they perform the national anthem before a MLB American League baseball game between the Oakland Athletics and the Seattle Mariners at Oakland-Alameda County Coliseum in Oakland, California on 25 September, 2017 Reuters/Stephen Lam American sportspeople kneel in protest Samaje Perine #32 and Chris Carter #55 of the Washington Redskins hold hands as they stand and kneel in unison during the national anthem before playing against the Oakland Raiders at FedExField on 24 September, 2017 in Landover, Maryland Patrick Smith/Getty American sportspeople kneel in protest Meghan Linsey, a former contestant on "The Voice," kneels after singing the national anthem before the start of the Tennessee Titans and Seattle Seahawks football game at Nissan Stadium in Nashville, Tennessee on 24 September, 2017 Ryan Hermens/The Paducah Sun via AP American sportspeople kneel in protest The Los Angeles Chargers are seen during national anthem before the game against the Kansas City Chiefs at the StubHub Center on 24 September, 2017 in Carson, California Jeff Gross/Getty American sportspeople kneel in protest Nick Kyrgios of Team World joined NFL stars from Wembley by dropping his knee before his Laver Cup match with Roger Federer today during his mens singles match against Roger Federer of Team Europe on the final day of the Laver cup on 24 September, 2017 in Prague, Czech Republic Julian Finney/Getty American sportspeople kneel in protest Laremy Tunsil #67, Maurice Smith #27 and Julius Thomas #89 kneel with Jarvis Landry #14 of the Miami Dolphins during the National Anthem prior to an NFL game against the New York Jets at MetLife Stadium on 24 September, 2017 in East Rutherford, New Jersey Steven Ryan/Getty American sportspeople kneel in protest Tampa Bay Buccaneers Wide Receivers Mike Evans #13, and DeSean Jackson #11, take a knee during the national anthem before the game against the Minnesota Vikings on 24 September, 2017 at U.S. Bank Stadium in Minneapolis, Minnesota Hannah Foslien/Getty American sportspeople kneel in protest Denver Broncos players kneel during the American National Anthem before an NFL game against the Buffalo Bills on 24 September, 2017 at New Era Field in Orchard Park, New York Brett Carlsen/Getty American sportspeople kneel in protest Buffalo Bills players kneel during the American National anthem before an NFL game against the Denver Broncos on 24 September, 2017 at New Era Field in Orchard Park, New York Brett Carlsen/Getty American sportspeople kneel in protest Colin Kaepernick #7 and Eric Reid #35 of the San Francisco 49ers kneel in protest during the national anthem prior to playing the Los Angeles Rams in their NFL game at Levi's Stadium on September 12, 2016 in Santa Clara, California. The kneel began as a protest against police killing people of colour Thearon W. Henderson/Getty American sportspeople kneel in protest Megan Rapinoe #15 kneels during the National Anthem prior to the match between the United States and the Netherlands at Georgia Dome on 18 September, 2016 in Atlanta, Georgia Kevin C. Cox/Getty

Mr Trump later said the recent "protests have nothing to do with race" and that players who took a knee during the national anthem at games on 24 September were disrespecting the flag and the country.

It was not until after Mr Trump's Alabama rally remarks when several more players throughout the league began taking a knee as well or locked arms with teammates - white and black - during the anthem.

The Seattle Seahawks and Tennessee Titans opted to stay in the locker room ahead of their game that week.

The NFL had issued a statement in response to Mr Trump's initial comments that said: "divisive comments...demonstrate an unfortunate lack of respect for the NFL, our great game and all of our players, and a failure to understand the overwhelming force for good our clubs and players represent in our communities."

Even NFL owners who are vocal supporters of the President like the New England Patriots' Bob Kraft disapproved of the President's comments. Mr Kraft said he was "deeply disappointed."

Mr Trump and surrogates held to the line that kneeling during the anthem was an insult to the US military and the country, however, several veterans and members of Gold Star families - those who have lost a loved one in the military - have spoken out against this notion.