Celtic manager Neil Lennon is concerned full-back Adam Matthews may have fractured his collarbone in the 2-0 home win against Motherwell.
Matthews found himself on the wrong end of a sliding challenge by Motherwell captain Keith Lasley and was stretchered off early in the match.
"First and foremost, I think it was a penalty," said Lennon.
"He landed badly on his shoulder, it could be a fractured collarbone, which could see him out for quite some time."
The victory against Stuart McCall's side sent Celtic back to the top of the Scottish Premiership table and maintains their undefeated run in the league.
However, Lennon was upset to lose a player who has been a Champions League starter.
Welsh international Matthews was stretchered off and replaced by James Forrest, with the home manager taking a dim view of the challenge from Lasley.
"He got his leg in first and got the ball on the follow-through," said Lennon.
"He's at the hospital at the moment and we're just waiting on the result, but early signs are not good."
Despite the injury to Matthews, Celtic won comfortably, with impressive strikes in either half from Anthony Stokes and Kris Commons.
And Lennon was satisfied with the response to Tuesday's home defeat by Barcelona in the Champions League.
"I'm more delighted with the performance of the team today," he explained
"Against a very good Motherwell team, it's an exceptional performance.
"Looking at the players yesterday, you could see they were all in good condition, and I think they were just looking forward to getting out there and playing again.
"We controlled the game and some of the chances we created were great.
"I think the fans got good value for money. It could have been more, but I'm thrilled with a clean sheet too."
He singled out the afternoon's two goalscorers for their contribution to the win, and remarked that Commons had demonstrated a moment of inspiration.
"I thought they were the two best players on the pitch, although Virgil van Dijk and Efe Ambrose would run them close," said Lennon.
"Stokes is playing very well and when Kris gets into those little pockets, he's a supremely intelligent, tactical player.
"His goal was a flash of genius. I really enjoyed watching it, I could watch it again and again."