The veteran has been fined $13,369 by the NFL for giving the middle finger as he was carted off the field in last Sunday's victory at the Arizona Cardinals, according to a Seattle Times report.
Thomas, who held out all offseason in protest of his contract situation and returned without a new deal, was carted off the field with his leg in an air cast midway through the third quarter. He gave the middle finger in what appeared to be the direction of Seattle's sideline as he was being taken into the locker room.
Because the act occurred outside the field of play, no penalty was assessed during the game. However, in fining Thomas, the league determined the moment should be considered unsportsmanlike conduct, the Seattle Times reported.
"I don't know exactly what the intention of that was," Seahawks coach Pete Carroll told KIRO-AM 710 ESPN Seattle on Monday. "I didn't see it and I don't know what the intention was there, and I'm not jumping to conclusions on that. There's nothing for us to talk about at this point."
Thomas has taken heat for the gesture, but Carroll said people need to cut the 29-year-old "a little slack."
"People that are criticizing whatever happened don't understand," Carroll said. "This was an earth-shattering moment for a kid. He's trying to play this game he loves and all of sudden this happens again. He knew exactly what happened to him, so he went right to what it's going to take to get back."
ESPN's Brady Henderson contributed to this report.