Newcastle United's injury problems continue to mount following the news that Steven Taylor faces eight weeks on the sidelines.
Defender Taylor has undergone a hamstring operation which the club confirmed on Tuesday will keep him out for "a couple of months".
"Massadio [Haidara] and Jack Colback have knocks. Papiss Cisse has had a problem with his back since West Ham," McClaren said.
With Newcastle's only win of the campaign so far coming in the League Cup against Northampton Town, McClaren is desperate for a morale-boosting result on Wednesday as the pressure mounts on his position.
"Sheffield Wednesday are a good team I know well from last season", said the former Derby County boss. "They've got good players who can hurt us.
"We've got the experience, patience and calm to deal with the current situation. We need to build belief and confidence.
"Tomorrow is a massive game. We've got to go out there and perform, and set ourselves up for Saturday [against Chelsea]."
