Newcastle United midfielder Bruno Guimaraes suffered an ankle injury in victory over Fulham.
The Brazil international left St James' Park on crutches and with his right foot in a protective boot after rolling his ankle in the first half against the Cottagers.
Toon manager Eddie Howe said: “He was in distress, and he was worried about his ankle after the game too. It was a twist. He felt he could carry on until right at the end of the first half when he signalled to come off.
"That's never a good sign from our perspective, and we'll have to get it scanned and checked out, and see what the damage is. We hope it's not long term, but at this moment in time, we don't know."
When asked if he should have been withdrawn earlier, with Bruno needing help up the tunnel and leaving the field in tears, Howe said: "Should he have come off a bit earlier? Yeah, probably, with hindsight.
"But the player wanted to stay on and I always tend to go with the player as long as it's not a concussion. The players know how difficult the Premier League is, and they know their bodies better than I do.
"He was probably limping for five minutes or so at the end of that first half, but it's always a difficult one, right on half-time, to make a change. You like to try to do that in the calm of half-time to make a proper decision. He played very well in the first half, despite the injury."