Barcelona sporting director Txiki Begiristain admits the loss of playmaker Lionel Messi to injury is a huge blow.

The Argentinian ace was substituted at the end of the first half of Saturday's 3-0 win at Valencia after suffering a thigh injury that Spanish media are reporting could keep the 20-year-old sidelined for a month.

Barca have already ruled Messi out of next weekend's 'el clasico' against league leaders Real Madrid at the Nou Camp, with Begiristain admitting: "It is the worst thing that could have happened.

"He is a player that gives us balance and is in great form. We hope to se him recover very soon. As well as wanting to see him make a quick come back, we want him to come back fully fit," added Begiristain on his club's website.

Messi scored a hat-trick in last season's corresponding fixture against Real, which finished 3-3, and Barca striker Samuel Eto'o said: "It is a pity to lose him because at the moment he is our best player."

The Cameroon striker struck twice in the first half against Valencia as the Catalan giants secured their first league win on the road since September.

It also lifted them to within one point of arch-rivals Real ahead of their home match against Osasuna on Sunday evening.

"I hope this 3-0 win will give us confidence to win the upcoming games, both home and away," Eto'o said.

"We need to go into the game against Madrid with calm. We have to prepare well for the game."

(reopens) A statement on the Barcelona website confirmed Messi would be sidelined for between four and five weeks

"If this estimated time out is served the player will miss between five and seven Barca games," said the statement.