Steve Bates is of the opinion Spain striker Fernando Torres will continue to struggle to make an impact at Chelsea.
The 27-year-old arrived at Stamford Bridge in a £50m deal from Liverpool in January but has failed to regain the sharpness that frightened the world's best defences prior to a major knee operation in April 2010.
Bates said: "I just don't think he's the player he was. Mentally and physically he's not the player he was.
"I saw him at Old Trafford a couple of seasons ago, maybe slightly longer, and he absolutely terrorised Nemanja Vidic, who that season was heading for Player of the Year.
"That game alone lost Vidic the Player of the Year that season - up to then he'd been comfortably winning. Torres was absolutely sensational that day. That player's just gone. He has had injuries but it's in the head. Having said that, I'm not sure Chelsea play to his strengths."
With the Blues in a transition phase with many of their big names pushing or past 30, Bates has been impressed by the calmness of new manager Andre Villas-Boas.
The Portuguese followed in the footsteps of compatriot Jose Mourinho this summer by leaving Porto to take the Chelsea reigns, and 10 points from his first four games in charge represent a solid start for the precocious 33-year-old.
Bates said: "Villas-Boas looks assured and confident in himself. I've been in his press conferences after matches and he's got a great brain. I can see he's got a vision of how he'd like things to be.
"It's going to take a while for him to get there. He's a very impressive character but of course we haven't really seen him under much pressure as of yet.
"Chelsea have only played the likes of Sunderland, Norwich and West Brom and this clash with United at Old Trafford is his first biggest test of the season."