Liverpool’s injury crisis has deepened with the confirmation that Albert Riera and Yossi Benayoun are likely to be out of action for up to a month.

The midfield duo limped off during Liverpool’s 2-2 draw with Birmingham City on Monday night having suffered hamstring injuries.

Rafael Benítez, the Liverpool manager, admitted after the game that he feared the worst and scans have revealed that both players have suffered hamstring tears.

Riera had missed Liverpool’s previous five matches with a hamstring problem and his return to action against Birmingham had been a boost for Benítez. The fact that the Spain international has suffered a recurrence will come as a bitter blow, particularly with the in-form Benayoun receiving an almost identical injury.

In the next four weeks Liverpool face a testing fixture programme at home and abroad with Barclays Premier League matches against Manchester City, Everton and Blackburn Rovers, and Debrecen and Fiorentina in the Champions League. Benítez is now facing the possibility of going into those games without several of his senior stars.

Fernando Torres has begun a rehabilitation programme aimed at curing a longstanding groin problem and the Spain forward could be unavailable for up to two weeks. Daniel Agger is undergoing treatment on a back problem that forced him to withdraw from the Denmark squad. The club’s medical staff are assessing the extent of the calf strain that led to Glen Johnson pulling out of Fabio Capello’s England party for Saturday’s friendly against Brazil in Doha, Qatar.

Torres’s predicament will inevitably attract the most attention given his status as one of the world’s best attacking players. Benítez, though, is refusing to put any pressure on the club’s top goalscorer this season, stressing that Torres will return only when fully fit. “We will see how he reacts,” Benítez said. “We are not considering an operation yet.”

Torres’s absence against Birmingham allowed Benítez to give David Ngog, the French forward, a starting place and the 20-year-old repaid his manager’s faith with an enterprising performance, albeit one that was overshadowed by his role in winning the controversial penalty that led to Liverpool’s equalising goal.

Ngog is hoping to feature more prominently in Benítez’s team and believes that working under the Spanish manager and alongside Torres can only improve him as a player.

“I am desperate to prove to the manager that I am ready to play in any situation,” Ngog said. “At training every day, I can feel some improvement in my game. It would be hard not to with so many great players around me.”

• Chelsea were also dealt an injury blow yesterday when it emerged that José Bosingwa, the defender, will be out for about three months after he had surgery on his left knee.