CLEVELAND (AP) — JC Tretter’s days blocking defensive linemen are over. He’s not through going up against the NFL.

The former Cleveland Browns center and current NFLPA president announced his retirement on Thursday, saying on Twitter that he ended a playing career that started in Green Bay and spanned nine seasons “on my own terms.”

However, Tretter said in an interview that he believes his work with the union played a role in him not being re-signed after the Browns released him in March.

“There are teams right now that I would say are desperate for a center based off how camp’s going,” Tretter told Sports Illustrated. “Still no calls.”

Tretter, who plans to stay on and serve his second term leading the union, missed only one game for Cleveland over the past five seasons despite playing on bad knees. He rarely practiced so he could get treatment but always managed to be ready for games.

The 31-year-old didn’t miss a snap until last season, when he tested positive for COVID-19 before a Christmas game in Green Bay.

“Incredible how he was able to fight through injuries and all of those type of things,” Browns coach Kevin Stefanski said. “Just think about some of the injuries he dealt with in Green Bay and then came here and did not miss much time — I don’t even know if he missed any time.

“Never wanted to come out of the game. An impressive example for the young guys about how to make it to Sunday.”

The Browns released Tretter — days after he was elected to a second term as president — in a salary-cap move. There had been speculation Cleveland might bring him back after starter Nick Harris suffered a season-ending knee injury in the exhibition opener.

However, the Browns elevated Ethan Pocic to the starting lineup and Tretter remained unsigned before deciding to retire.

Tretter was instrumental in setting up team COVID-19 protocols and helping the league navigate pandemic-related challenges during the 2020 season. He was also a strong advocate for player safety and believes some of that work resulted in him being shunned as a free agent.

While he was still playing, Tretter thought his efforts off the field would have an impact on his future.

“Guys would be like, ‘Oh, like how are your knees doing?’” Tretter told SI. “And I always said, ‘My NFLPA job is gonna end my career well before my knees end my career.’”

Green Bay drafted Tretter in the fourth round in 2013 out of Cornell. He broke his ankle during the offseason and didn’t play his first year. In 2014, he played in eight games, missing time with a knee injury.

He spent three seasons with the Packers before the Browns signed him as a free agent in 2017.

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