SANTA CLARA, CA - SEPTEMBER 12:  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.  (Photo by Thearon W. Henderson/Getty Images)
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SANTA CLARA, CA - SEPTEMBER 12: 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. (Photo by Thearon W. Henderson/Getty Images)
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(CNN) —  

Colin Kaepernick’s attorney Mark Geragos said Tuesday he has a “high degree of confidence” that he will be able to prove National Football League team owners colluded to keep Kaepernick from being signed.

“I am going to predict right now that we will have a smoking gun,” Geragos told CNN’s Anderson Cooper on “AC360.” “There are people who are not going to get into an arbitration proceeding and they are not going to lie. They are not going to lie. They are going to tell the truth and they’re going to say what happened. They were told no, you’re not going to hire him.”

Kaepernick, who is still a free agent, first took a knee during the singing of the National Anthem before a 2016 preseason game. He said he knelt to protest the treatment of black Americans, particularly by police.

Packers fans push for Kaepernick

The former San Francisco 49er filed the grievance on Sunday under the league’s Collective Bargaining Agreement, according to a statement from Geragos, who is also a CNN contributor.

How much could Colin Kaepernick win in his collusion case against the NFL?

The protest was seen by some as disrespecting the flag. Kaepernick has yet to be picked up by another team since opting out of his contract with the 49ers in March.

“It’s beyond any doubt that he should be playing in the league and that’s all he really wants,” Geragos said.

The NFL Players’ Association is not representing Kaepernick in this grievance. However, the association said it will be speaking with his legal team and will support him in his efforts.

Before the grievance was filed, NFL Commissioner Roger Goodell wrote in a letter to team executives that the league needs to “move past this controversy” over the National Anthem.

In the letter, which was obtained by CNNMoney, Goodell wrote that the dispute “is threatening to erode the unifying power of our game, and is now dividing us, and our players, from many fans across the country.”

Geragos was asked if the ultimate goal of the grievance is for Kaepernick to play in the NFL again or for him to receive a monetary reward.

“Colin said, ‘my No. 1 goal is – I’m 29 years old, I want to play,’” Geragos replied.

CNN Money’s Ahiza Garcia contributed to this report.