Last night's 1-0 win over Wigan means three more points at the Reebok Stadium on Saturday will take Sir Alex Ferguson's men to the summit for the first time this season.

No one at United is taking victory for granted, not least because of the injuries that threaten to leave Ferguson's strong squad severely weakened.

But O'Shea thinks a place at the head of affairs for a couple of days - before Monday's Merseyside derby - should focus a few United minds.

"It is a fantastic incentive," said the Republic of Ireland star.

"That was what we were talking about a few months ago when we had these games in hand.

"We felt if we could get to a stage where we could be top, having played the same number of games as everyone else, it is a definite advantage."

With Bolton generally a happy hunting ground for United - last season's defeat and finger-jabbing row between Ferguson and referee Mark Clattenburg excepted - and the Trotters' form having dipped in recent weeks, the visitors should be confident.

But having amassed what most pundits believe is the strongest squad in the Premier League, Ferguson is now fearing certain parts of it being decimated.

Rio Ferdinand, Patrice Evra and Wes Brown are definitely missing from a defence that has now kept a club record nine successive clean sheets in the top flight - with Jonny Evans possibly joining the casualty list after limping through virtually the full 90 minutes last night.

If the Northern Ireland star does not make it, Ferguson would be forced to push either Gary Neville or O'Shea alongside Nemanja Vidic.

Either move creates a headache, because Neville has played only a handful of league matches at centre-half in his entire career - while for O'Shea to move inside, Ferguson would presumably have to hand a debut to Fabio Da Silva, who played in a closed-doors friendly with Bradford earlier this week.

The striking berths are equally problematic, because Wayne Rooney has been ruled out for at least three weeks with a hamstring injury - and Carlos Tevez's state of fitness is also a concern.

Rooney's absence includes the FA Cup fourth-round tie with Tottenham, plus Premier League meetings with West Brom and Everton in addition to the Bolton trip and next Tuesday's Carling Cup semi-final against Derby.

While United can cope with that, any extension to the present recovery timescale brings England's friendly against Spain on February 11 and the Champions League meeting with Jose Mourinho's Inter Milan at the San Siro two weeks later into view.

Rooney's spell on the sidelines is compounded by the knowledge that his almost certain replacement, Tevez, spent most of last night's win limping - after being caught by a thunderous Titus Bramble tackle.

Having waited so long for a decent run in the side, Tevez would be cursing his luck if he was unable to make the most of Rooney's misfortune - although at least Ferguson would be able to rely on Cristiano Ronaldo's abilities as an orthodox striker alongside Dimitar Berbatov if he was without two of his leading men this weekend.

"Bolton will be another difficult away game," O'Shea predicts.

"They will definitely be up for it. They will see that we only got past Wigan by one goal and maybe get some confidence from that.

"It will be hard. But we will be up for the battle."