"The fact that they didn't have Robben in the side made a big, big difference," said City manager Kevin Keegan, whose side are the only team to have beaten Chelsea in the league, 1-0 in October.

Chelsea's lead in the standings was reduced to nine points over second-placed Manchester United [ Images ] with 12 games to go.

Robben suffered a foot injury just before scoring in Chelsea's 1-0 win at Blackburn Rovers on Wednesday and watched from the Stamford Bridge [ Images ] stands on Sunday.

Chelsea fear Robben's foot may be broken although they will not know the true extent of the damage until he has undergone a scan once the swelling has gone down.

"I just don't know," Mourinho repeated several times to persistent questions about the injury.

The versatile Robben, a roving winger, has been a key player in Chelsea's drive towards the Premier League title, scoring seven goals in 14 league games since recovering from a previous foot injury.

"I accept that Robben is a magnificent player and any team will miss a magnificent player," Mourinho said.

He was reluctant, however, to accept that the absence of Robben and striker Didier Drogba [ Images ], who has scored eight league goals and is nursing a bruised thigh, had a bearing on the result.

"In terms of creativity and quality of play, I think so, but even without them we had enough chances to score goals and win the game," he said.

"So I prefer to say that my players in finishing situations were not lucky and in David James [ Images ] (City) had a goalkeeper who made some incredible saves."