The price for the victory, which gave Barca a 4-2 aggregate win over the Scots, was yet another injury to talismanic striker Lionel Messi.

The 20-year-old left the Nou Camp pitch in tears late in the first half, after tearing a muscle in his left thigh.

It was the fourth time the Argentinian has suffered this type of injury in the last three seasons. The last time saw him sidelined for five weeks earlier this season.

Two seasons ago, it forced him to miss Barcelona's Champions League final victory over Arsenal in Paris.

Messi's game relies heavily on his explosive acceleration and naturally, this has heightened concerns about the latest blow.

'We saw him crying and that affected us,' midfielder Deco said. 'There is nobody like him, but he is very young and I am sure that he will be back very soon.

'It has taken the focus off a night when we have completed our task.'

Coach Frank Rijkaard had come under media fire for leaving Messi out of Saturday's 2-4 league defeat at Atletico Madrid.

Barca captain Carles Puyol now believed the press was partly to blame for the injury.

'Messi's injury is a lesson to everyone,' he said. 'You pressured for him to play against Celtic and now look what has happened.

'Now, I suppose you will be criticising the medical staff because he is injured.'

Messi will almost certainly miss the Champions League quarter-finals early next month, and six Primera Liga matches, as Barca look to close a five-point gap between themselves and Real Madrid.

The diminutive star - the 2007 World Player of the Year runner up - has been Barca's most effective striker this season. He scored nine goals in La Liga and six in the Champions League.

Midfielder Xavi Hernandez, who scored the third-minute goal, admitted that the loss of Messi was a big blow to the club's prospects.

'We paid a very high price for this victory,' he said. 'Leo was in fantastic form. It is a real shame.'

Barcelona's opener on Tuesday came as a result of a stunning combination, which showed off their players' mutual understanding of each other.

Ronaldinho, standing on the edge of the area, flicked a pass to his left while looking in the other direction and Sylvinho flew down the flank before crossing to Xavi.

The Spanish international then volleyed the ball over the head of Celtic's Polish goalkeeper, Artur Boruc, to take his tally to five goals in his last seven matches.

'The ball did move in a weird manner, but I would save that kind of attempt nine times out of 10,' said the £10 million (S$27.9 million) Boruc, taking the blame.

'I just don't think I was good enough.'

Xavi's strike took the wind out of the sails of the Scottish side, who were perhaps conscious that getting three goals without reply in the Nou Camp was an almost impossible target.

REUTERS