OXNARD, Calif. -- Zach Thomas understands the perception some people have after his abbreviated final season in Miami, though he doesn't agree with it.
"They labeled me with that, as prone for concussions," he said. "Everybody just thinks I'm some guy out here that's punch drunk, running around."
Now Thomas looks forward to the opportunity to prove them wrong.
If he seems confused at times during the Dallas Cowboys training camp, that is because Thomas is trying to learn and adjust to a new defense -- not aftereffects of a concussion and migraines that limited the seven-time Pro Bowl linebacker to five games last season.
"I wouldn't be here if it was going to be a problem," Thomas said. "Trust me, there's no difference between 12 and 13 years to me. I could have retired and did all that."
Thomas did go home to Texas, to play in the state where he was a high school and college standout before his 12 seasons with the Dolphins. He gets to be part of a legitimate Super Bowl contender and the chance to finally win a championship.
Even before playing a game for the Cowboys, Thomas has earned the respect of his new teammates and given them a glance of what he's still capable of doing.
"He makes me practice harder, definitely running around trying to keep up with him," said Bradie James, the other starting inside linebacker and the Cowboys' leading tackler the past three seasons. "Even though this is his 13th year in the league, he hasn't slowed down a bit."
The biggest adjustment for Thomas is playing in a 3-4 defense after being the middle linebacker in 4-3 sets at Miami, where he had at least 100 tackles his first 11 seasons before last year. Thomas still had 52 tackles in the five games he played last year.
"It is a different position, a different mentality," Thomas said. "But it's still football. You've just got to run and tackle the guy with the ball."
James already envisions himself as the bruiser in a powerful 1-2 combination with Thomas, who turns 35 the week of the Cowboys' season opener.
"If I can knock down an O-lineman, knock down some running backs, he'll definitely tackle whoever has the ball," James said.
Thomas was released by the Dolphins in February as part of a massive rebuilding project overseen by new vice president of football operations Bill Parcells. Miami was 1-15 last season.
In the third game last September, against the Cowboys, Thomas sustained a concussion that forced him to miss two games. Then after a loss to New England on Oct. 21, his vehicle was rear-ended and he didn't play again, placed on injured reserve against his wishes in December because of nagging migraines.
The seemingly obvious conclusion was that the concussion played a factor in his health issues after the accident.
"They tried to put two and two together," said Thomas, insisting that "it just was more of a sinus problem" related to a deviated septum.
Coach Wade Phillips said there are no limitations on Thomas, and that the linebacker isn't being monitored any differently than the rest of the players.
Thomas had missed only 13 games his first 11 NFL seasons, never because of a concussion. The most games he had missed in a season was five, because of an ankle injury in 2000. His 168 starts in Miami were the most ever for a Dolphins defender.
His debut with the Cowboys comes Saturday night in the preseason opener at San Diego. Thomas has no concerns about the increased physical contact and extra hits that will come in game after two weeks of training camp.
"I've been taking hits," Thomas said. "I'm serious, when you take on big guys like [353-pound offensive guard] Leonard Davis and all that."
Still, Thomas expects to feel some anxiety before the game.
"I've never really gotten nervous for preseason games, but I'm sure I will because I'm in a new uniform," Thomas said. "It will probably be like my rookie year. Just get that out of the way and let's play football."
Rookie TE Martellus Bennett, a second-round pick out of Texas A&M, missed Thursday's only practice. Owner Jerry Jones said Bennett was dealing with a "personal thing." Jones wouldn't elaborate but said it was not a health issues. Bennett is with the team and expected to play Saturday. ... Jones said the Cowboys aren't interested in released New York Jets quarterback Chad Pennington as a possible backup to Tony Romo.