West Ham United boss Sam Allardyce expects a difficult FA Cup encounter with Manchester United.

United are expected to make several changes for the late-afternoon kick-off, but Allardyce does not expect that to weaken the Premier League leaders at all.

He said: "We are not under the same pressure as we are in the Premier League that is for sure, but we have a responsibility because there will be a full house at West Ham tomorrow, live on TV so we have to put the best team out we have available.

"I am sure (United manager) Sir Alex (Ferguson) will make some changes, but it will not really make much of a difference because at the moment any changes he does make, they still keep winning.

"They are in top form, so it will be hugely difficult, but it is a fantastic one to be involved in and if we can create a bit of an upset it would be a great bonus to make it into the next round."