Mohamed Sissoko's career hangs in the balance with fears growing that the Liverpool midfielder may lose the sight in his right eye after he was kicked in the head during the Champions League defeat by Benfica in Portugal, writes Dominic Fifield

The Mali international suffered serious damage to his retina when Benfica's midfielder Beto raised a boot and inadvertently connected with the stooping Sissoko's head after some 30 minutes at the Estadio da Luz on Tuesday night.

The 21-year-old, clearly in distress, was taken off on a stretcher having also suffered a deep cut to his forehead. But the principal concern was his sight.

Sissoko returned from Lisbon yesterday with the club doctor Mark Waller, having spent the night at the CUF Hospital in the Portuguese capital under observation. He underwent a CAT scan and other tests in Lisbon which confirmed the damage to the retina before his journey home, though further examinations are needed to ascertain the precise extent of the damage.

"He's undergone specialist care here but we are reserving judgment," said Dr Joao Paco, the hospital's clinical director.

Although Sissoko was deemed fit enough to travel back to Merseyside, concerns are rising over the extent of the injury and the implications it could have for his career. He will undergo further tests today to determine if the retina is detached and he requires surgery.

"The injury is still affecting his eyesight," confirmed a Liverpool spokesman yesterday. "Further consultations with eye specialists have now been arranged in the United Kingdom."

At the very best, Sissoko's impressive first season in English football since his £5.6 million summer signing from Valencia appears to have been ended.

Beto, who was booked for his challenge, was apologetic in the aftermath. "I just caught him accidentally with my boot and unfortunately it opened up a wound," he said. "I want to apologise to him because I did not mean to injure him. It was just a typical midfield challenge, the sort that happens all the time.

"You are always getting 50-50 balls like that and all you are thinking about is trying to win it. All I saw was the ball and I put my foot in to try and nick it away from him. I certainly did not mean to do him any harm and I am very concerned to hear he has ended up in hospital.

"I tried to apologise to him at the time, when he was receiving treatment, and I want him to know I am really sorry."

Sissoko will surely be missed for the return leg at Anfield as the defending champions attempt to haul back a 1-0 deficit.