Thomas, who missed the entire preseason in a contract dispute with the Seahawks, did not report to the team until Wednesday.
"He had a good week," Carroll said of Thomas on Friday. "He was solid all week long. He was fired up and studying and working hard at it and he had a good week."
Thomas is entering the final season of a four-year, $40 million deal he signed in 2014. He wrote in The Players Tribune that he believes he should be paid significantly more than the $8.5 million base salary he's due this year.
A three-time first team All-Pro, Thomas declined to speak to reporters Friday. He gave his reasons for returning on an Instagram post earlier this week.
"(I) worked my whole life for this. ... I've never let (my) teammates, city or fans down as long as I've lived and don't plan on starting this weekend," wrote Thomas. "With that being said, the disrespect has been well noted and will not be forgotten. Father Time may have an undefeated record but best believe I plan on taking him into triple overtime when it comes to my career."
Seattle's secondary underwent major upheaval during the offseason. Star cornerback Richard Sherman was released and standout safety Kam Chancellor announced he was walking away from the game due to a neck injury.
In addition, the Seahawks placed cornerback Dontae Johnson on injured reserve Saturday and waived cornerback Byron Maxwell with an injury settlement.