The Ghana international is battling a hamstring injury ahead of Saturday's Barclays Premier League clash with Wigan in which the Black Cats will attempt to end a 10-game run without a win.
Bruce said: 'John Mensah has got a bit of a nick in his hamstring and we will see how he is in the next 24-48 hours. But he is an obvious doubt.'
Battling: Sunderland's John Mensah challenges Louis Saha of Everton
If Mensah misses out, that would leave Bruce having to field a 15th different line-up at the back this season.
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