The Stamford Bridge outfit sit nine points clear of Tottenham and Arsenal at the top of the table, with United a further six points back in sixth, albeit with a game in hand.
"I think Arsenal and Manchester United [are the biggest title rivals]," he told Sky Sports .
"United had a bad first part of the season and I think for a couple of games now, they played well.
"They drew against Stoke, but they have good players and the squad is very good. The manager is good, so they will be second or third.
"Tottenham also are strong. We lost there, but for me it is more Manchester United. They are more experienced. That is my opinion, maybe I'm wrong."
Chelsea tightened their grip on top spot with a draw against Liverpool on Tuesday and could move further clear when they host Arsenal on>