Nike unveiled a new ad on Monday for the 30th anniversary of its "Just Do It" campaign featuring Colin Kaepernick, who has remained unsigned by an NFL team for nearly two years.

The former San Francisco 49ers quarterback tweeted an image from the new campaign featuring a close-up photo of his face, accompanied by the words "Believe in something, even if it means sacrificing everything."

Kaepernick became the first player to take a knee during the national anthem during the 2016 NFL season as part of an effort to protest social injustice. He became a free agent at the end of the season, and has remained unsigned.

ADVERTISEMENT

The player has since filed a grievance alleging that league owners colluded to keep him off a team. An arbitrator ruled last week that Kaepernick's case will go to trial.

ESPN reported that Nike signed Kaepernick to an endorsement deal in 2011, and has maintained that contract since then.

"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," Gino Fisanotti, Nike's vice president of brand for North America, told ESPN.

In the roughly two years since Kaepernick first started kneeling, numerous other players have taken a knee, raised a fist or have stayed off the field during the playing of the national anthem in protest of social injustice.

President TrumpDonald John TrumpHannity urges Trump not to fire 'anybody' after Rosenstein report Ben Carson appears to tie allegation against Kavanaugh to socialist plot Five takeaways from Cruz, O'Rourke's fiery first debate MORE has lashed out at protesting players, declaring they should be fired and suggesting they don't belong in the country.

NFL owners initially caved to pressure from Trump and his supporters earlier this year when they approved a policy that will fine players who kneel during the anthem. However, the league has since put that policy on hold.