Ferguson refuses to point finger at fragile defence

It is just one of those high-scoring seasons, says manager of United's failings at the back

For a manager whose championships have been built on rock-solid defence – just 24, 22 and 27 goals conceded in the past three title-winning seasons – Sir Alex Ferguson's explanation yesterday of his side's sudden defensive fallibility was odd.

"You have to look at the number of goals scored in the Premier League this season as opposed to the previous season," Ferguson said. "It's the most there's been, maybe we are just in one of these unusual seasons." Granted, 319 goals scored against 299 at the same period last season but Manchester United are not one of those sides whose defence is supposed to cave in.

It has hardly been an avalanche of balls bulging in their own net – in the league United have shipped 11, as opposed to nine at the same point last season – but none of their six clean sheets have been against distinguished opposition and the frailties exposed by Manchester City, Sunderland, Liverpool and then CSKA Moscow in midweek augur ill for the meeting with Didier Drogba and Chelsea tomorrow. Carlo Ancelotti's side, incidentally, have kept nine clean sheets and conceded only one goal on the way to maximum points at Stamford Bridge this season.

For their part, United have started with 12 different defences in Premier League and European competition, if you include the goalkeeper. Ben Foster's eight-match Premier League run deputising for Edwin van der Sar contributed to the poor communication, which has seemed so uncharacteristic, and the Dutchman's return has coincided with Rio Ferdinand's collapse in form, which has led some to a fundamental reappraisal of the defender.

Both Ferguson and Wes Brown have admitted this week that Ferdinand has been playing while injured and there was a worrying prognosis yesterday from the manager, who said United are baffled as to why he cannot recover from a calf injury which has seen him missing since Fernando Torres gave him the runaround at Anfield two weeks ago.

"We don't know exactly where the calf injury is coming from, whether it is coming from the lower back or whether it's a nerve thing," Ferguson said. "Calf injuries are usually two to three weeks, but there's no sign of him recovering from this injury. We're looking at the whole situation – whether or not it's coming from the back – but in the meantime he's out. There's no improvement, put it that way, so we're looking at something different."

With none of last Tuesday's back four – Gary Neville, Brown, Jonny Evans and Fabio da Silva – looking comfortable, United can take some heart from Nemanja Vidic's expected return from a calf injury tomorrow – possibly alongside Evans with Brown switching to right-back as United attempt to repel the vibrant Drogba, 12 goals to the good in all competitions.

Vidic's dismissal in the 2-0 defeat at Anfield overshadowed a big display in which he seemed intent on demonstrating that Torres does not have the Indian sign over him and went some way to achieving that. Meanwhile, Brown is still playing his way back in after the last injury-ravaged season.

Ferguson's rather unconvincing support of his side's rearguard also included the suggestion that the dubious defending against CSKA was a product of his side experimentation . "In a way we experimented a little bit," Ferguson said. "It didn't particularly work but in saying that, by being so open we've created 10-12 chances in the match. It's the devil and deep blue seas sometimes. We were open because of it and we won't be as open on Sunday I hope."

United's poor record at Stamford Bridge – one win in 11 and that came in April 2002 – and the prospect of Chelsea opening a five-point lead at the top – will make sure of that.

Titanic battles: Best of Chelsea v United

*15 Aug 2004 – Chelsea 1 Man Utd 0 Jose Mourinho's first game in charge ends in victory, courtesy of Eidur Gudjohnsen's 15th-minute goal.

*10 May 2005 – Man Utd 1 Chelsea 3 Ruud van Nistelrooy scores early, but Chelsea win with goals by Tiago, Gudjohnsen and Joe Cole.

*29 April 2006 – Chelsea 3 Man Utd 0 Chelsea clinch their second successive title thanks to goals from William Gallas, Ricardo Carvalho and Joe Cole. Mourinho throws his medal to fans.

*24 Sept 2007 – Man Utd 2 Chelsea 0 Avram Grant's first game in charge ends in defeat with goals from Carlos Tevez and Louis Saha.

*11 Jan 2009 – Man Utd 3 Chelsea 0 Nemanja Vidic, Wayne Rooney and Dimitar Berbatov settle this one-sided contest. Luiz Felipe Scolari is sacked a month later..........  Mark Fleming