Chelsea coach Jose Mourinho has revealed Robben is to undergo surgery and that is likely to keep him out for the remainder of the campaign.

The winger returned from international duty with Holland yesterday afternoon and medical staff decided that surgery was the best option to cure the problem.

Chelsea's season has been blighted by long-term injuries to key players including captain John Terry, goalkeeper Petr Cech and England midfielder Joe Cole.

Mourinho tried to put a brave face on the loss of the winger but found it difficult to believe he had lost his services after an international week when he had played twice for his country.

Mourinho told Chelsea TV: "Robben will be out for a long time. For me it is a bit difficult to accept because he played two matches for his country, 90 minutes last Wednesday, and the next day he came here and he is injured.

"He needs surgery and we lose an important player maybe for the rest of the season."

The actual scale of the knee problem has yet to be revealed by Chelsea but if it involves ligament damage, then Robben is unlikely to take any further part in their quest for glory on three remaining fronts - the Barclays Premiership, FA Cup and Champions League.

The Dutchman's season has been peppered with injuries and this latest setback could not have come at a worse time for Mourinho.

Robben had been on top of his game prior to the international break and Mourinho had been full of praise for the winger who had been instrumental in helping keep the pressure on Manchester United at the top of the Premiership.

But while Mourinho lamented the loss of the mercurial Robben, he was boosted by the return of Cole.

Cole has been sidelined all season with a broken foot but now the England midfielder is ready to help Mourinho get over Robben's absence.

Mourinho declared: "Joe Cole is coming back and maybe next week we have him. But again we can never have our best team with every player available. But if I can lose one and gain one, it is not so bad.

"At this time we just want to have no more injuries because the matches are arriving and all of them are like finals.

"We want to be under pressure and being under pressure is to play every three days. We have fought a lot to be in this situation. It is difficult but we cannot complain, we need to be happy.

"What a player like John Terry wants to do now is play and play and play and don't miss one single second because he missed so much in the season.

"We have some very strong characters and if they are not injured, they want to play every time."

Cole has targeted next week's Champions League clash with Valencia at Stamford Bridge as his comeback game but that might be a little too early for the England star.

However, there is every indication he could return for the second leg at the Mestalla.