"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."
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."