Sunderland boss Steve Bruce is awaiting the results of a scan on captain Lee Cattermole's hamstring injury.
Cattermole is struggling with the back-related hamstring problem which hampered him last season and he is a doubt for Saturday's game against Blackburn Rovers.
The midfielder is an influential performer for the Black Cats and Bruce is hoping it will not prove to be a serious injury.
Bruce said: "He is away for a scan at the moment. We hope it's nothing too sinister.
"It's a bit of an issue and a bit of a worry."
The Black Cats boss is counting the cost of the busy festive period after Asamoah Gyan, Nedum Onuoha and Danny Welbeck picked up injuries in Tuesday's 2-0 home defeat by Blackpool.
Welbeck is expected to be fit for the New Year's Day visit of Blackburn, but Bruce is unsure if Onuoha and Gyan will be available.
He added: "Both Onuoha and Cattermole are huge doubts for Blackburn, Gyan is also a big doubt.
"I can't comprehend playing games in 13 days. Asking you to play that many games takes its toll and we've picked up injuries. That's the downside to playing that many games in quick succession."