Former San Francisco 49ers quarterback Colin Kaepernick is taking a stand against NFL owners.

Various media outlets are reporting that Kaepernick is filing a lawsuit against NFL owners for colluision.

The 29-year-old free agent has attained the services of high-profile lawyer Mark Geragos, and is filing under the collective bargaining agreement, according to Bleacher Report.

Kaepernick was the first player in the NFL to protest during the US national anthem, sitting down during the rendition of 'The Star-Spangled Banner' prior to San Francisco's pre-season outing against the Green Bay Packers in August last year.

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Despite a classy season with an underperforming 49ers outfit, Kaepernick opted out of his contract, and has received little interest and no offers from the remaining 31 franchises throughout the league.

ABC reports that Kaepernick's lawsuit claims owners "colluded to deprive Mr. Kaepernick of employment rights in retaliation for Mr. Kaepernick's leadership and advocacy for equality and social justice."

New York Giants co-owner John Mara has denied Kaepernick was being rejected by NFL clubs, despite receiving a multitude of letters from fans voicing their disapproval of the former University of Nevada star.

"Anybody that thinks that there's been any conversations going on among teams about Colin Kaepernick is crazy," Mara said on ESPN Radio in August.

"That just is not the case. I saw a quote, I think it was [Dolphins owner] Steve Ross recently that said, 'Teams want to win so badly that if they believe a player can help them win, they're going to bring him on.'

"I think there are certain issues obviously that go along with Colin Kaepernick and that may have scared some teams away, but there is absolutely no blackball going on here. I just don't see that at all."

Mara went on to suggest that Kaepernick would go on to be signed, but the 2013 Super Bowl runner-up is still unsigned, despite a plethora of quarterbacks across the league getting injured.

Aaron Rodgers of the Green Bay Packers is the latest to have suffered an injury, with the 2011 Super Bowl winner breaking his collarbone against the Minnesota Vikings this morning (NZT).

However, NFL commisioner Roger Goodell has denied any claims that the league has plotted against signing Kaepernick.

"I believe that if a football team feels that Colin Kaepernick, or any other player, is going to improve that team, they're going to do it," he said in June.