"Yes, we will make a few changes for the cup tie," he said. "The likes of Patrice Evra and Michael Carrick, we took them off as soon as we got the third goal.

"They deserve a break and they have played in all the games. We'll have a look at the situation. We've got fresh players.

"Young Shinji [Kagawa] came in. We've got plenty of players to freshen it up."

United have picked up eight wins in their past nine Premier League matches, with a 1-1 draw at Swansea City the only blemish in that run.

But the United manager says last season's collapse, which saw United lose an eight-point lead over the course of the final six games, means he will not take the advantage at the top of the table for granted.

"Over the years, December has been a good month for us. This time it has put us into a seven-point lead with 17 games left," he said.

"It's not what I would say is a healthy lead, but it is a lead. It gives us something to kick on with. We just don't want to make mistakes like we did last year."

Manchester City manager Roberto Mancini has suggested that the arrival of Robin van Persie has been the difference in the title race to this point.

The Dutchman, 29, who joined in a £24 million deal from Arsenal, added weight to that argument by taking his tally to 16 league goals for the season with a brace at the DW Stadium.

Ferguson said he always expected Van Persie to be a success.

"I knew he would make the difference because of his maturity, because I made the point at the time: he has great international experience, he's played for Arsenal for seven years, and he came to us at the very peak of his career," he said.

Javier Hernandez scored United's other two goals.