Stephen Elliott damaged ankle ligaments last night and is now facing a fitness battle ahead of the Republic of Ireland's European qualifier away to Cyprus in three weeks time.
The striker scored in Sunderland's 3-0 win over struggling Leeds United at Elland Road but limped off with half an hour remaining.
Elliott will definitely miss the club's match with Leicester City this weekend but it is unknown quite how long he will be sidelined for.
The 22-year-old was a 43rd minute substitute for compatriot David Connolly who suffered a thigh strain and will also miss the Leicester match.
Republic of Ireland boss Steve Staunton, who could also be without defender Stephen Kelly, will monitor Elliott's situation closely over the next fortnight as he considers the make-up of his squad.
Kelly is still struggling with the calf injury which forced him to miss the recent defeat to Germany and his club, Birmingham City, don't expect him to play for another three weeks.
:quality(70)/cloudfront-eu-central-1.images.arcpublishing.com/irishtimes/YVIRIOZQ35EWRPZXR27KGMO6YU.png)