GREEN BAY, Wis. -- Jimmy Graham's return to Seattle left him with a broken thumb that could sideline him for at least part of the remainder of the season.

Tests on Friday showed the Green Bay Packers tight end broke his thumb, a source told ESPN's Adam Schefter. The team is trying to figure out how long Graham will be out.

Graham, who signed with the Packers this offseason after three years with the Seahawks, left in the first half of Thursday's 27-24 loss and did not return.

The extent of Graham's injury was first reported by NFL Network.

The Packers used Lance Kendricks almost exclusively in his place, but coach Mike McCarthy said rookie Robert Tonyan, who caught a 54-yard touchdown in the first half for his first career NFL reception, could see his playing time increase if Graham misses significant time.

"Robert's definitely ready," McCarthy said. "It's really just a product of who's in front of him. ... Yeah, he's ready to play. I thought he really came on there at the end of training camp, and he's done a lot of good things. ... We have confidence in Robert."

The Packers (4-5-1) play again next Sunday night at Minnesota.

McCarthy did not say whether Graham could play against the Vikings.

"I don't have the exact extent of the injury, so I'm sure he'll answer that next week for you," McCarthy said. "... He came through the training room. He's in there right now."