Sunderland manager Steve Bruce fears striker Kenwyne Jones could be facing at least one month on the sidelines.
The Trinidad and Tobago international headed the Black Cats into an early lead with his eighth goal of the season in Sunday's Premier League clash at home to Manchester City.
But he was then forced off at half-time with a groin injury as City battled back to claim a 1-1 draw.
Bruce said in his post-match television interview that he did not know how long Jones would be on the sidelines, but he now fears the forward will be unavailable for around four weeks.
"We were just getting up a head of steam and getting a settled team and another one of our big players looks as if he is going to be out for at least a month," said Bruce.