If Zach Thomas decides to play a 13th NFL season, it will almost certainly not be with the Miami Dolphins.

Thomas, a seven-time Pro Bowl linebacker and one of the most popular and productive players ever to wear a Dolphins uniform, was released Thursday, the biggest move yet in Miami’s massive rebuilding project.

“I have a tremendous appreciation and admiration not only for the Dolphins organization, but for the fans as well, for all of the support that they have given me,” Thomas said in a statement, in which he thanked owner Wayne Huizenga, new football operations head Bill Parcells and general manager Jeff Ireland.

The 34-year-old linebacker said he plans to play with another team next season. There’s always a chance he could re-sign with Miami, although that seems, at best, doubtful.

“I am healthy and look forward to playing in 2008, but will always consider myself a Miami Dolphin,” Thomas said.

The team made Thomas aware of the decision Thursday morning.

“Zach Thomas has been a great player on this team for many years,” Ireland said. “And because of the type of player and the kind of person that Zach is, this was not an easy decision.”

Thomas missed most of last season because of concussions and migraines and was placed on injured reserve against his wishes in December because of nagging migraines, an aftereffect of an Oct. 21 car crash.

The move is the second major salary slash this week by the Dolphins, who went 1-15 last season and subsequently brought in Parcells to lead the rebuilding.

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Miami trimmed about $9 million in 2008 base salary on Monday, when it parted ways with quarterback Trent Green, wide receiver Marty Booker and seven other players. Thomas was slated to make just over $5.6 million in base salary this coming season.

Thomas was the 154th player chosen in the 1996 draft, and many observers didn’t give the 5-foot-11 player from Texas Tech much chance of making the Miami roster.

From there, he only wound up one of the best linebackers in Dolphins history.

Thomas led the Dolphins in tackles 10 times, is the franchise’s all-time leader in that category by a wide margin, and his 168 games is the most by any Miami defensive player.

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“In addition to his numerous accomplishments on the field, he was a leader off of it as well,” Ireland said. “We want to thank Zach for everything he has done for the Dolphins organization and the South Florida community.”

He was remarkably durable in his first 11 seasons, missing only 13 games, and recorded a career-best 165 tackles in 2006 — an indication he wasn’t exactly slowing down.

But Thomas missed two games in September this season because of a concussion, and on Oct. 21, he took another hard shot off the field. Thomas had eight tackles in Miami’s 49-28 loss to the New England Patriots, and as he and his wife drove home that day, their vehicle was rear-ended on Florida’s Turnpike.

Originally, the Dolphins said Thomas was uninjured in that crash. But he experienced numerous migraines following that wreck, and never got back on the field in 2007.

He was inactive for the next seven games before the Dolphins put him on injured reserve, officially ending his season and sparking widespread speculation that his time with Miami could be drawing to a close.

A week ago, new Dolphins coach Tony Sparano said no decisions had been made about Thomas’ status for 2008.

“We’re doing what we have to do,” Sparano said on Feb. 7 when asked about Thomas’ future.