Colin Kaepernick thanks first two players to kneel during national anthem
"My Brothers @kstills and @ithinkisee12 continue to show their unwavering strength by fighting for the oppressed!," Kaepernick said in a Twitter post accompanied by a picture of the two players kneeling.
"They have not backed down, even when attacked and intimidated. Their courage will move the world forward!
"Love is at the root of our resistance!"
The issue has remained in the spotlight with U.S. President Donald Trump highly critical of the protesting players.
The NFL owners in May approved a rule requiring players to either stand on the field for the anthem or remain in the locker room, but the policy is on hold pending discussions with the NFL Players Association.
Kaepernick is no longer in the league but remains in the headlines.
He voices a new Nike commercial that was unveiled during the first game of the NFL season between the Philadelphia Eagles and Atlanta Falcons on Thursday.
If Kaepernick is not backing down as the leader of the player protest movement, then neither is Trump.
On Sunday morning, Trump tweeted a reference to U.S. television ratings for Thursday's game, which started late due to bad weather.
"Wow, NFL first game ratings are way down over an already really bad last year comparison," Trump said.
"Viewership declined 13%, the lowest in over a decade. If the players stood proudly for our Flag and Anthem, and it is all shown on broadcast, maybe ratings could come back? Otherwise worse!"