Wayne Rooney admits Andy Carroll is likely to pose a threat in Wednesday's Barclays Premier League encounter at Old Trafford.
West Ham's loan signing from Liverpool got off the mark for his new club with a consolation effort in Sunday's 3-1 defeat at Tottenham and is likely to be the focal point for many of the Hammers' attacks.
Rooney has worked with Carroll at international level and thinks the £35million hitman will pose problems for the United back four.
"Andy Carroll is a handful," said Rooney. "I am sure if you ask any defender, they find it difficult to play against someone like that who is good in the air and on the floor. He is physical and he makes it difficult. That type of player doesn't always get all the goals but they can cause trouble up front and create problems. I am sure that is what Sam Allardyce wants him to do."
The Reds go into the West Ham clash top of the table after Manchester City and Chelsea played out a goalless draw at the weekend.
"We know City and Chelsea will be looking out for our results as we look out for theirs," accepted Rooney. "But it is important for us to concentrate on our own performances and make sure we get the wins because there are a lot of games coming up. It is tough. I am sure the manager will use his squad. It will have to come through for him."