Steve Bruce has revealed that Lorik Cana was withdrawn from action on Saturday after tweaking his groin.
The Sunderland skipper was in line to be on the bench against Tottenham Hotspur at the Stadium of Light, but pulled up in the warm-up.
Having limped from the field, a decision was quickly taken to remove him from the matchday squad.
Cana had been struggling with a groin complaint in the build-up to the game and appeared to aggravate the injury while being put through his paces.
With plenty of important games to come, Bruce admits he was reluctant to risk further inflaming the problem by sticking with his captain.
The Black Cats boss remains unsure as to whether the Albanian midfielder will be fit enough to travel to West Ham on Saturday, but is prepared to give Cana as long as necessary to shake off the knock.
"Lorik felt sore in the week and he felt it again in the warm-up," Bruce told the club's official website.
"I won't risk anyone at this stage of the season. We'll see how he is in the week."