The cornerback said Wednesday he aggravated his twice-repaired right ACL last week but did not suffer any tears or any serious injury.
"Aggravated is the best to put it," Thomas said of what happened to his knee after he slipped while trying to cover Domenik Hixon. "An ACL is so simple. It's either working or it's not. And mine is still working, so, thank God. Something happened which caused it to swell."
Thomas says he feels no pain and there is no swelling in his knee at the moment. He will begin rehabbing his knee but has no timetable for a potential return.
"I think it's all dependent on my leg," Thomas said. "I think it's something that can be three weeks or something that can be eight weeks, to be honest with you. I think the Giants want to be very cautious.
"The big picture is the long run, the rest of the season, get into the playoffs."
Thomas tore his ACL last year in a preseason game against the Chicago Bears and rehabbed vigorously to come back. It was the second time he had torn his ACL in his career after first injuring it in 2005 while at USC.
During a practice on July 29, Thomas slipped while covering Hixon and experienced swelling the next morning. The Giants sent him to undergo an MRI at the Hospital for Special Surgery in Manhattan, where the Giants' doctors saw an injury of some sort to his ACL.
After visiting with Giants physician Dr. Russell Warren, Thomas flew to the West Coast to see Dr. Arthur Ting, who repaired his ACL last fall. Thomas sought a final opinion from Dr. James Andrews, and the consensus from all three doctors was that he could rehab his knee, avoid surgery and attempt to play again this season. Thomas said he only had one MRI and did not need to undergo an arthroscopic procedure to determine the damage to his knee.
"I think this is just a minor scare more than anything," Thomas said. "The ACL was still intact in the MRI, but the way it felt in their hands -- which is the true test -- it felt a little bit loose compared to what it was a couple of days ago. That's why Dr. Warren was so concerned.
"As the week went on, the knee didn't swell any more. "It actually went back down. If (I) tore (it), it would be swelling up a lot with all the flying (cross country) and traveling. And the strength was still there. I never had any pain or weakness or anything. They came to a consensus that there's no reason to go in there to scope to find if there's anything wrong."
Thomas said he felt frustration after the setback but never experienced anger like he did last preseason when his season ended so quickly.
He had suffered a minor back injury a few days earlier in practice and believed that helped lead to aggravating his ACL.
He still has hopes of playing in the season opener against Dallas but understands he must take things slowly. Until then, the Giants will look at Prince Amukamara as a possibility to start in place of Thomas. Michael Coe, Justin Tryon and Bruce Johnson are veterans who also could have an opportunity to play more. Third-round pick Jayron Hosley has also impressed in recent practices.
"I don't plan on having any more setbacks," Thomas said. "If I can be out there, I want to be out there. I'm not going to jeopardize my career for the rest of the season and I don't think the Giants want me to do that as well.
"I never heard anybody really aggravating their ACL or stretching it out and kind of having a timeline. It's not like I tore my MCL and it takes four weeks to heal. I truly don't know. It's really based on how my knee feels and how I react to the rehab."
Asked if he has any doubts about playing again this season, Thomas said, "Not at all."