Thomas tested a brace on his injured elbow in Friday's practice and is listed as questionable for the game at Wembley Stadium. He has caught 11 passes for 148 yards and a touchdown in three games this season.
"He's got a little bit of stiffness in there, so it's a matter of what can he do?" Jaguars coach Gus Bradley told reporters Friday of Thomas. "What can we ask him to do? We want to make sure if he plays we're putting him in position to be successful. I think that's the question."
If Thomas can't play, the Jaguars would have just two healthy tight ends -- 11-year veteran Marcedes Lewis and second-year player Neal Sterling. Ben Koyack had surgery last week to repair a damaged MCL in his knee.
The Jaguars also listed linebacker Dan Skuta (hip) as questionable. Defensive end Dante Fowler Jr. (shoulder) practiced fully on Friday and is probable.
As expected, Colts coach Chuck Pagano ruled out wide receiver Donte Moncrief (shoulder), offensive lineman Jonotthan Harrison (appendectomy) and defensive back Darius Butler (hamstring) for the London game. Wide receiver Phillip Dorsett (ankle) and offensive linemen Joe Reitz (back) and Denzelle Good (back) are listed as questionable.