Three-time Pro Bowl left tackle Tra Thomas is retiring.
Thomas, 35, said Saturday that he has decided to leave the game because he can no longer play at the level he expects from himself.
He recently had arthroscopic knee surgery, and he said he hasn't performed well during this camp.
He signed with San Diego in June as a possible replacement for Marcus McNeill, who is holding out.
"I was just watching film and I don't think I was playing as well in practice as I should be," said Thomas, who entered the NFL as a first-round pick of Philadelphia in 1998. "If I'm not playing well in practice, I'm not going to play up to my standard in a game ... I feel very good about the decision. I 'm going out on my own terms. At least, I know I gave it everything I could."
Thomas was a first-round draft pick of the Philadelphia Eagles in 1998. He went to the Pro Bowl after the 2001, '02 and '04 seasons. He played in five NFC Championship Games and one Super Bowl with the Eagles.
He signed with Jacksonville last year and played in just eight games, starting one.
He said he appreciates the chance San Diego gave him, but he thought it was best to leave the game.
"I could have milked it for a year," Thomas said. "But I have too much respect for the game to do that."
McNeill is unhappy that he hasn't been given a long-term deal. Instead, the Chargers tendered the restricted free agent a one-year deal for $3,168,000. Because he didn't sign by June 15, the Chargers were entitled to slash his pay to 110 percent of his 2009 base salary, or approximately $630,000.
General manager A.J. Smith placed McNeill and San Diego's other holdout, Pro Bowl wide receiver Vincent Jackson, on the roster exempt list Friday. That means they'll be suspended for three games once they sign their contract tenders.
For Saturday night's exhibition game against Dallas, the Chargers were down to second-year pro Brandyn Dombrowski and undrafted rookie Nick Richmond at left tackle, the spot that protects quarterback Philip Rivers' blind side. Second-year pro Tyronne Green has played at left tackle, but sat out Saturday night with an ankle injury.
Jackson also is unhappy he hasn't gotten a long-term deal. The Chargers recently gave the Seattle Seahawks permission to talk to Jackson's agents, but the player's price tag apparently remains too high.
Jackson, coming off his second straight 1,000-yard season, already has been suspended by the NFL for the first three games for violating the league's substance abuse policy. He pleaded guilty in February to his second DUI since 2006.
Bill Williamson covers the AFC West for ESPN.com. Information from The Associated Press was used in this report.