Colin Kaepernick has been revealed as one of the faces of Nike's new "Just Do It" ad campaign, two years after kneeling during the United States national anthem to protest against racial injustice.

The 30-year-old quarterback, who opted out of his contract with the San Francisco 49ers in 2017 and remains unaffiliated to any NFL team, tweeted a black-and-white photo of himself featuring the Nike logo and “Just Do It” slogan as well as a quote: “Believe in something. Even if it means sacrificing everything.”

Nike retweeted Kaepernick's post, but representatives for Kaepernick and the NFL have not yet commented.

"We believe Colin is one of the most inspirational athletes of this generation, who has leveraged the power of sport to help move the world forward," said Gino Fisanotti, a Nike vice president of brand for North America, according to ESPN.

Nike has endorsed Kaepernick since 2011 but has not featured him in campaigns since his departure from the NFL.

The decision to feature Kaepernick so prominently in the advertising campaign for the 30th anniversary of Nike's “Just Do It” motto is likely to prompt a reaction from some NFL fans, as well as President Donald Trump, who has said he would love to see NFL owners fire football players who disrespected the American flag.

News of Nike's ad campaign broke just days before the first game of the NFL season on Thursday, when the controversy over pre-game protests could flare anew.

This season, the NFL has adopted a rule requiring all players to stand during the anthem, although it gave them the option of staying off the field until the ceremony was over. Even so, the protests have persisted through the preseason and the NFL has said it is in discussions with the players union on the policy.

In 2016, Kaepernick became the first NFL player to take a knee in protest of growing racial disharmony across the United States, including police shootings and instances of police brutality

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

"I am not going to stand up to show pride in a flag for a country that oppresses black people, and people of colour," Kaepernick said in a press conference after first sitting out during the anthem. "To me, this is bigger than football, and it would be selfish on my part to look the other way. There are bodies in the street, and people getting paid leave, and getting away with murder."

Mr Trump's anger towards the protesting players prompted more to join, in-turn morphing the demonstration into something of direct resistance to his administration's handling of race issues.