Thomas lost his job to rookie Melvin White after allowing a 63-yard completion that was called back because of a penalty and a 73-yarder that wasn't in last week's 30-15 victory over the St. Louis Rams.
Coach Ron Rivera indicated on Wednesday that White would get the start, but not that Thomas would go from starter to inactive.
"Melvin White has done a really nice job,'' Rivera said. "JT (Thomas) is struggling with it right now.''
White was signed as an undrafted rookie out of Louisiana-Lafayette. He had an interception and forced fumble in Week 3 against the New York Giants when Thomas was out with a concussion suffered against Buffalo.
Thomas, fifth on the team in tackles, had been solid against the run but susceptible in the passing game.