Colin Kaepernick was not invited to NFL talks about player protests during the national anthem despite other players wanting him there, his lawyers said.
The NFL met team owners and player representatives in New York on Tuesday.
It hailed "productive" talks but no concrete steps to address the issue were announced.
Quarterback Kaepernick first sat down during the US national anthem in August 2016, before opting to kneel instead, in protest against racial injustice.
Other players followed suit, and the movement spread after criticism from US President Donald Trump last month.
Kaepernick, 29, has been without a team since he opted out of his contract with the San Francisco 49ers in March.
He has filed a grievance against team owners he believes are conspiring not to hire him because of his protests.
"Colin Kaepernick was not invited to attend today's meeting by any official from the NFL or any team executives," his lawyers said in a statement.
"Other players wanted him present and have asked that he attend the next meeting with the goal of forging a lasting and faithful consensus around these issues. Mr Kaepernick is open to future participation on these important discussions."
In an earlier joint statement with the players' union, the NFLPA, the league said it had been agreed that promoting equality was among "common issues", and pledged to meet again "to continue this work together".
"As we said last week, everyone who is part of our NFL community has a tremendous respect for our country, our flag, our anthem and our military," the statement read.
"In the best American tradition, we are coming together to find common ground and commit to the hard work required for positive change."