Thomas had non-football related surgery a couple of days into camp and missed a good portion of the next three weeks.
But he returned to practice recently and was full-speed on Thursday night, leading the Cardinals in tackles with seven in a 70-14 blowout of Charlotte at Papa John's Cardinal Stadium.
"It felt so good to be out there," Thomas said. "When it first happened to me, we were iffy on the first game and thinking more of the second game. But I felt really good and it felt good to be out there.
"I have been just trying to get better every week, working on my conditioning a lot."
The 6-foot-1, 232-pound Thomas had five solo tackles and played a good portion of the game, He started the game at inside linebacker, but with Louisville playing its dime defensive package a lot in the first half he didn't see a ton of snaps.
Thomas said he was "just very happy to be our here" with his teammates.
"Stacy's a really good football player and he has been for the last two years," U of L coach Bobby Petrino said. "He's been a big part of our football team. It's great to have him back and going.
"He's one of our smartest players out there. He understands what the offenses are trying to do and he's going to make a lot of plays for us."
Thomas helped lead a defense that held Charlotte to 0-for-13 on third downs and to just 208 yards of total offense.
"We have been working real hard," Thomas said. "There's still a lot of work to do for us as a defense."