Manchester United boss Sir Alex Ferguson insists he has no concerns over his defence leaking goals.
Ferguson has stressed Rangers cannot be underestimated by a side who have already thrown away winning positions twice this season.
"We don't have frailties," he said. "It has been a lack of concentration in our defending.
"People say this is a mismatch but they said that about Barcelona on Saturday night.
"Football throws up surprises. We are never going to forget Rangers' history and this will be a tough game.
"I know Walter Smith personally and he has worked with me twice. I know how astute he is and how good a tactician he is. I can almost see that little brain working at the moment."
