Sir Alex Ferguson feels Chelsea will present the biggest threat to a Manchester United Premier League title hat-trick.

The Red Devils open their campaign against Newcastle on Sunday with few expecting anyone other than the 'big four' to be challenging at the top.

Ferguson agrees with that view. And while he respects Liverpool and Arsenal enough to be wary of their challenge, it is Chelsea who worry him the most.

"Arsenal had a great run last season until they got injuries in March, while Liverpool have signed Robbie Keane and one or two others," said Ferguson.

"But Chelsea are the most experienced and they might be our biggest threat."

Not that Ferguson is spending too much time considering the strengths of others. He is more concerned about the improvement of his own side.

As United won the Premier League last term and then thrillingly captured the Champions League trophy in the Moscow rain with a penalty shoot-out win over Chelsea in May, it would not appear they can get much better.

Yet Ferguson is convinced they will.

"We don't need to get much better to achieve what we did last season but the challenge for us is to improve," he said.

"You would think with young players like Anderson, (Cristiano) Ronaldo, (Wayne) Rooney and Nani we have the capacity to do that.

"I am expecting a natural progression and there is no doubt in my mind this team will win championships long after I have left.

"There is a good foundation here now."

One of Ferguson's key men, overlooked as Ronaldo has risen to prominence so startlingly, is Rooney.

The England striker's 18 goals last term did not even come to half the 42 Ronaldo contributed to United's success.

Yet Rooney may not deserve the tag of underachiever which seems to have been pinned on him so ruthlessly by the critics.

So often last term the 22-year-old found himself shunted into wider positions. And Ferguson has pledged to use his strengths to much greater effect.

"We have to be fairer to Wayne this season," he said.

"He is such a willing performer that you are always tempted to listen to him at times.

"He says he could play centre-midfield, centre-half, goalkeeper. If you ask him to do a job, he will - no problem.

"That is the kind of individual you are dealing with. He has that great desire to play anywhere."

For all his achievements, the same cannot really be said of Ronaldo.

Yet Ferguson is expecting more from the Portugal international when he eventually returns to action after ankle surgery.

With October already pencilled in as his comeback month, Ronaldo is hard at work on his rehabilitation programme.

And Ferguson has detected no festering issues over the winger's previously-stated desire to join Real Madrid.

"There has been no problem with Cristiano at all, he has slotted straight back in," he said.

"The specialist was most surprised at the condition Cristiano is in," he said.

"He is ahead of schedule, so he will be in rehab for the next three weeks, then he will move on to endurance work and serious running before he goes onto the football side with us."