Sunderland have doubts over injury-prone Ghanaian defender John Mensah ahead of the trip to Liverpool on Saturday in the English Premier League.Mensah limped out of the 1-1 draw against Aston Villa on Wednesday night with a knee injury and the central defender is rated as doubtful for the Anfield clash.Black Cats boss Steve Bruce will make a late check on the defender but Paulo Da Silva, who replaced him at Villa Park, is on standby to come in should he be ruled out.The on-loan Olympique Lyon player has been a worry injury to the Sunderland technical set-up and that seems to be the hinderance to his stay extension. Source: Ghanasoccernet.com