Spain midfielder Andres Iniesta has signed a contract extension with Barcelona to keep him at the club until 2015.

The new deal increases Iniesta's buy-out clause to 200million euros and ties him to the Catalan giants for the next five and a half years with his new deal running until June 30, 2015.

The 25-year-old has received an improved deal in return for extending his contract by a year and upping the buy-out clause by 50million euros.

Barca have also been boosted ahead of Sunday's big match with Real Madrid by the participation of injury doubts Lionel Messi and Zlatan Ibrahimovic in today's training session.

Messi (thigh) and Ibrahimovic (hamstring) missed the midweek Champions League win over Inter Milan as a precaution but are still doubts for the weekend.

Meanwhile Xavi has demanded Barca remain faithful to their attacking philosophy by dictating the game against their bitter rivals - and insists the league leaders' tactics "do not interest him".

After seeing the capital club depose them at the summit of La Liga last weekend, the Catalans began a crucial week with an impressive 2-0 win over Inter on Tuesday.

With top spot and the ever-crucial head-to-head record at stake when Madrid come to the Nou Camp on Sunday, Spain's 'El Gran Clasico' is attracting more headlines than ever.

Despite hammering Madrid 6-2 at the Bernabeu last season en route to winning the league, Champions League and Copa del Rey, Xavi insists victory - and not the margin of it - is most important.

"We are not thinking about beating Real Madrid by many goals," he said.

"We want the three points and that is what we will go out to win. We have a lot of respect for them and we must be careful because historically these are complicated games.

"They are the leaders at the moment and they are scoring goals at the moment. But we are at home and we are highly motivated for the game.

"The clasicos are unpredictable games that are decided on small details," the Catalan playmaker continued.

"We have to try and dominate possession and play like we know how, which is to go forward. We want to play our own game and maintain the style that has brought us good results so far.

"We have our philosophy and how Madrid play does not interest me."

Barca's treble success, combined with Madrid's unprecedented recruitment drive in the summer, has ensured even more hype for this instalment of world football's biggest club clash.

Xavi, however, refused to gloat when asked about Madrid's habit of spending over the odds.

"I do not like to think like that," he said. "The teams both have their own ideas of how to play. Real Madrid were the victims of our success last season and now, with new players there, they are looking for their style of play.

"Now if I had to choose one of the philosophies I would say that I prefer ours."

Barca captain Carles Puyol has attempted to ease the pressure on his side by insisting the home team are not favourites.

"We have great respect for Madrid," he said. "They are league leaders and that means something. They have won nearly all their games and are a difficult side.

"I think our game with them is 50-50."