(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.

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.

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