First-choice full-backs Dani Alves and Eric Abidal both miss out through suspension, meaning Guardiola will have to reshuffle a back-line already missing several key components.

Mexico captain Rafa Marquez has been ruled out for the rest of the season with a knee injury, while Argentina defender Gabi Milito is still absent following more than a year on the sidelines.

That leaves just three senior central defenders available for Wednesday's match.

Of those, captain Carles Puyol and former United defender Gerard Pique are certain starters, but Uruguay centre-back Martin Caceres seems unlikely to feature after receiving scant playing time from Guardiola in recent weeks.

Caceres began the season as the club's fourth-choice centre-back, but Guardiola preferred to move holding midfielder Yaya Toure back into the side's defence for Barcelona's Champions League semi-final second leg against Chelsea.

Toure also played that role in the final of the Copa del Rey, when Barcelona thrashed Athletic Bilbao 4-1.

And the Ivory Coast midfielder now looks set to line up alongside Pique in central defence on Wednesday, with Puyol reverting to one of the full-back positions.

The Barca captain began his career as a right-back and was named the best player in Europe in that position in 2002.

"Puyol is versatile; he can play in central defence, on the right or on the left," Guardiola explained.

"You always know you will get total commitment from him and he won't let me down wherever I play him - it's possible he'll start at left-back, although I have several options."

Guardiola fielded a host of youngsters and fringe players in last night's 1-0 defeat to Osasuna, with Samuel Eto'o and Eric Abidal the only first-team regulars on show.

Abidal is suspended for Wednesday so his inclusion was logical. The France full-back began in central defence, however, and allowed Guardiola to give Sylvinho a run out at left-back.

The Brazilian looked composed before he was replaced after 50 minutes and is another candidate to start on Wednesday.

"Sylvinho is another option," Guardiola continued. "He's an experienced player and he has been a great servant to this club - he has also played in the Premier League and I would have no qualms about playing him on Wednesday."

Should Sylvinho start against United, Puyol is likely to switch to right-back.

Against Osasuna, Guardiola fielded youngster Victor Sanchez in that position, but the versatile 21 year-old, who played in nine out of the 10 outfield positions for Barca's youth side, suffered an injury to his left hand and will be out for the next four weeks.

"The injuries keep piling up and most of them seem to be in defence," Guardiola lamented.

But the Barca coach says the absence of key players such as Alves, Abidal and Marquez will allow others to shine.

"We would love Dani (Alves), Abi and Rafa to be available on Wednesday, but they're not so others will come in and do a job.

"It's a chance for those players and I am convinced we can compete with the guys we have available," he said.

Caceres has started several matches at full-back this season, while Mali midfielder Seydou Keita is another option on the left.

Guardiola is also sweating on the fitness of Thierry Henry and Andres Iniesta.

Henry has been sidelined since the club's amazing 6-2 win at Real Madrid at the beginning of the month, while Iniesta has been out with a thigh problem picked up a week later in the 3-3 draw against Villarreal.

Henry trained briefly with his team-mates on Friday, while Iniesta continues to work his way back with individual exercises in the gym.

Both players are expected to feature on Wednesday, though.

Having celebrated the league title in front of their home fans after the match against Osasuna, Guardiola says the players' minds are now firmly focused on beating United.

"Now we're all thinking about the Champions League final - we'll go there to try and win the game and bring the title back to Barcelona," he said.