Sir Alex Ferguson believes Rio Ferdinand's return to fitness will give his side a psychological edge going into Sunday's crucial match with Chelsea at Old Trafford. Ferdinand has been missing since suffering back spasms in the middle of December.

United have coped well without the England defender but Ferguson knows his return for the visit of Chelsea is a huge boost ahead of a game that promises to influence the outcome of the title race. "We are delighted to have Rio fit again and back in contention," Ferguson said. "He's been having spasms and has missed the last few games and that's given us an opportunity to get it settled down.

"He's trained for the past few days and feels fine. You always benefit from having your best players available and he's one of the best in the world. There's no question about that. We are lucky to have some good young players here to come in and replace him, but having Rio back makes a difference because of his stature and presence."

Ferguson has challenged United to make full use of their home advantage against Chelsea and take a significant step towards another Premier League title. Liverpool remain top on 45 points, with Chelsea three points adrift. United, with two games in hand, have 38 - a tally shared by fourth-placed Aston Villa.

"The two games in hand we have gives us an opportunity to close the gap [on leaders Liverpool]," Ferguson said. "There is no question those are important games and we have to take advantage of them.

"But we need to focus on the challenge of Chelsea first. Our home form this season and record has been great again. Chelsea have always had a good record at Old Trafford. This is a big game and we need to meet the challenge."

While Chelsea have spent millions since the arrival of Roman Abramovich, Ferguson insists he will not change his philosophy of building successful teams without breaking the bank at Old Trafford. "Chelsea changed the face of the Premier League and to win the title back off them was important for us," he said. "We are building a team here that should last for a long time. We know we can't match the spending power of Chelsea and have to identify young players. But it's about spending money the right way and finding the right balance for the team."