Sir Alex Ferguson's side host the Midlands outfit after losing to Wigan Athletic in midweek. However, McLeish admits that the defeat will have little bearing on the size of the task that his side face this afternoon.
"There are no dud teams," he said. "There are no duff teams in the Premier League.
"We will go to Old Trafford knowing, as has been said, that United are a wounded animal. We know the size of task we face.
"Sir Alex Ferguson has been down this road. We must be disciplined."
Manchester United currently lead the league by a couple of points.