Prolific Sweden striker Henrik Larsson is contemplating retirement after he tore a knee ligament in Barcelona's 3-0 Primera Liga victory over Real Madrid on Saturday.

Larsson, 33, told a Swedish newspaper he was uncertain about his future after keyhole surgery on Monday showed the injury could keep him out for six months.

"I can't say if I will continue or quit before I have all the cards on the table," Larsson told Helsingborg Dagblad on Tuesday.

"Right now everything is just so grim and tiring. There are a lot of thoughts moving through my head. I had really hoped it would not be so serious."

Barcelona president Joan Laporta said he had offered Larsson a renewal of his one-year deal after hearing of the expected layoff.

"I have offered a contract renewal to Larsson so that he can put his mind at rest during this difficult time," Laporta told Catalan television station TV3.

Larsson, who has scored 32 goals in 82 appearances for Sweden, signed for Barcelona at the start of the season after spending seven years at Celtic. At the time both parties said the contract could be extended for a further season.

The Spanish club had said on Monday  that the striker could miss the remainder of the season after tearing the anterior cruciate ligament in his left knee.

The extent of the injury was revealed by keyhole surgery performed by club doctors on the Swedish striker's knee on Monday to repair cartilage damage sustained during Saturday's Primera Liga victory over Real Madrid.

Barcelona's official website said Larsson had asked for any surgery on the torn ligament to be postponed, making it difficult to estimate how long the 33-year-old player would be out of action.

"By the player's express wishes definite surgery on the anterior cruciate ligament has been postponed," the club quoted a medical statement as saying.

Barcelona, who are at home to Larsson's former club Celtic in the Champions League on Wednesday, said the injury was at least as serious as those suffered by Larsson's team mates Thiago Motta, Gabri and Edmilson.

Brazil midfielder Edmilson suffered damage to the same ligament in his right knee early last month and was ruled out for at least six months.