They face a United side buoyed by last night's 3-0 win against Greek champions Olympiakos which booked their place in the Champions League quarter-finals.
Allardyce said: "It's going to be a really tough game and we'll have to be on top of our form to get anything out of it.
"Our efforts at home are what I've been focusing on with the players, the fact that we've won the last three home games on the trot and we have to try to maintain that if we can to overcome this little blip.
"We've had two away games in which we haven't picked up anything, so the focus is to maintain our home results and try our best to pull off a big result."
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