Liverpool's Momo Sissoko has suffered vision loss in his right eye from being kicked in the head during the 1-0 Champions League defeat by Benfica, a hospital official said on Wednesday.

Sissoko, a 21-year-old Malian midfielder, was released from Lisbon's CUF Hospital on Wednesday afternoon to return to England [Images], clinical director Dr Joao Paco said.

"The prognosis is guarded but vision is going to be compromised on the right side. If it's going to be 20 or 80 percent we can't say right now, it's premature. You have to wait for the next 48 or 72 hours," Paco said.

"He suffered a trauma with bruising of the eye. There was no apparent destruction of the structure."

Sissoko took a kick in the face from a high challenge by midfielder Beto who was booked.

Liverpool, the defending European club champions, said on their website that Sissoko's retina had been damaged in Tuesday's opening leg of the first knockout round and his sight was affected.

Paco said Beto had been following Sissoko's case and was shaken by the injury.

LUISAO WINNER

Liverpool lost the match at the Stadium of Light when Brazilian defender Luisao headed the only goal six minutes from time. The second leg is at Anfield on March 8.

"For Liverpool the Champions League is important. I don't know why they left [captain Steve] Gerrard or [striker Peter] Crouch on the bench," Benfica coach Ronald Koeman said.

"There are other coaches besides me that would bet on rotating. But they suffered their first loss in the Champions League and right now we're a little bit more favoured.

"It could be that with this result we have more chances. They're greater than they were before the game," he told reporters.