Wes Hoolahan is a major doubt for Ireland's Euro 2016 Group D qualifier with Scotland in Celtic Park next month.
Norwich City star Hoolahan had to be helped off the pitch in the second half of their 1-0 defeat to Fulham with an ankle injury.
Canaries manager Neil Adams said the initial signs were not promising in terms of recovery.
Adams said: "He's in a protective boot, obviously we'll have to look at him and scan him, but he said straight away that it wasn't a great one.
"Fingers crossed on that, but it doesn't look too good at the minute."
Hoolahan recently played in Ireland qualifiers, starting and scoring in the 7-0 thumping of Gibraltar and then coming on as a substitute against Germany and providing the cross that led to John O'Shea's dramatic equaliser in the 1-1 draw in Gelsenkirchen.
Martin O'Neill's Ireland side meet Scotland on 14 November in Glasgow.