The astute Middlesbrough boss, speaking after his side's battling defeat at the Bridge last night confimed Chelsea's title credetials.
"Chelsea are the clear favouruites," admitted McClaren.
"But Arsenal and Manchester United will be waiting should they slip up. It's a three horse race now.
"Chelsea have being very fortunate that they have not lost key players through injury - men like (John) Terry, (Claude) Makelele, (Frank) Lampard and (Arjen) Robben.
"Chelsea can only lose the title now," he added.
The Blues opened up a seven point gap at the top of the league from Arsenal with two goals from Didier Drogba in a two minute spell in the first half.