Aston Villa defender Olof Mellberg has backed United's bid for the title and says Cristiano Ronaldo will be a key player in staving off Chelsea's challenge.

Martin O'Neill's men could have a big say in the shape of the title race as they face United twice in the Premiership either side of the turn of the year whilst taking on Chelsea on 2 January.

"It is going to be between United and Chelsea for the title," said Mellberg. "But United have looked really powerful so far."

The in-form Swedish defender has been playing at right back this season, but that position could see him up against either Ryan Giggs or Ronaldo, two United players he has great admiration for.

"It would be nice to face Ronaldo," he said, before adding: "But maybe it would be a good game to maybe move back into the centre!

"Ronaldo has done really well this season. If you follow his performances, he is a top class player and he has shown that in previous seasons as well as during this one.

"He is really quick and skilful with the ball at his feet and he will probably get a lot of free-kicks as well. We have to be aware of him."

But Ronaldo isn't the only in-form United player capable of causing damage at Villa Park.

"He is a great player and United also have Ryan Giggs who can operate in that position as well," Mellberg added. "We need to be on top of our game against them."