Javier Mascherano was injured in the first leg and will be missing for around six weeks as he joins Carles Puyol and Adriano on the sidelines. So who should take his place?

ERIC ABIDAL



MARC BARTRA

SERGIO BUSQUETS

ALEX SONG

SWITCH TO THREE AT THE BACK

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By Ben Hayward | Spanish Football WriterAs usual, Lionel Messi stole the headlines. The Argentine attacker scored the opening goal for Barcelona in the first leg of the Catalans' Champions League quarter-final at Paris Saint-Germain last Tuesday but was withdrawn at the interval with a hamstring strain which left hearts in mouths for fans of the Blaugrana.However, Messi's muscle problem turned out to be only minor and after missing Saturday's stroll at home to Mallorca in La Liga - which Barca won 5-0 in the absence of their finest footballer - and the Argentine is expected to be back in the team on Wednesday as the Catalans host PSG at Camp Nou.Of more concern to coach Tito Vilanova is the defence. Another Argentine, Javier Mascherano, was injured at the Parc des Princes and the converted centre-back will be sidelined for around six weeks with ligament damage. He will miss Wednesday's match, along with captain Carles Puyol (who has recently undergone a knee operation) and Adriano (close to a return from a hamstring injury but unlikely to be risked in this one).That leaves Gerard Pique as the only senior central defender fully fit and available for the Champions League clash and gives Vilanova a selection headache ahead of the game at Camp Nou. Here,takes a look at the options open to the Barca boss for their last-eight match on Wednesday.This would be some story but it could also be an unnecessary risk. Eric Abidal made an inspirational return to the Barcelona first team on Saturday as he replaced Pique for the final quarter of the Catalans' 5-0 win over Mallorca in La Liga.Abidal had been out for over a year after undergoing a liver transplant last April and only returned to football in a friendly for Barca B last month. Whether he is physically prepared for the rigours of a Champions League quarter-final against players of the calibre of Zlatan Ibrahimovic and Ezequiel Lavezzi is doubtful, yet he looked assured on Saturday - albeit against a poor Mallorca side who were already five goals behind - and Tito Vilanova's assistant Jordi Roura did not rule out the Frenchman for the PSG game on Wednesday. "He gives us another option," the coach told reporters. But it surely remains a risk.Marc Bartra began alongside Pique on Saturday and produced a polished performance in the centre of the Catalan defence, although the Blaugrana back line was rarely tested by a mediocre Mallorca team in one of the poorest displays in recent memory from a visiting side at Camp Nou.The 22-year-old Bartra featured only fleetingly when Barca were in a defensive crisis earlier on this season and it seems Vilanova has doubts over his long-term role in the first team. Considered by some to be too similar to Pique he has nevertheless impressed when selected and, if Abidal is not ready to step in, the La Masia graduate is the only natural defender Barca can call upon to partner Pique on Wednesday. However, in what is likely to be a tough physical battle at Camp Nou, his fragile frame may count against him.Barcelona often struggle in defence at set pieces due to a lack of height but, if Sergio Busquets partners Pique on Wednesday, the Catalans will boast two tall centre-backs who - in theory at least - would be expected to cope with the aerial threat posed by Ibrahimovic et al.Busquets has had mixed fortunes as a centre-back in the past, making mistakes last season in the position, and should he drop deep to help out on Wednesday then Barca will be deprived of one of the world's finest defensive midfielders. However, his tactical reading of the game and frame could persuade Vilanova to ask the pivot to partner Pique on Wednesday.If Busquets does start at the back, the improving Alex Song will almost certainly be the man to take his place in midfield, especially considering Mascherano is out injured. But it could be the other way around, with Busquets in midfield and Song at the back.The Cameroonian was signed as cover for both positions and has featured only sparingly this season, but he has filled in at times at centre-back, a position he also played at Arsenal, and represents an intriguing option for this match. Strong, athletic and faster than Busquets, the African's qualities may be better suited to a physical battle, although Barca would lose out in terms of height.Another alternative for Barcelona is to play with a three-man back line, although this would require huge discipline from the trio of defenders selected and could be a risk in a tight knock-out match against a dangerous counterattacking team.Jordi Alba has shown in the past he is capable of such control. The Spain left-back was excellent in a more defensive role against AC Milan last month. Dani Alves is unlikely to be chosen at the back in such a system, however, while Martin Montoya is also more of an attacking full-back and may not be trusted in a game of such magnitude. That means, therefore, that one of the above would probably need to fill in alongside Pique and Alba anyway.