Sir Alex Ferguson is set to look to Gerard Pique to solve the defensive crisis caused by Rio Ferdinand's injury.
Ferdinand left Middlesbrough yesterday with his left foot in a protective plastic casing and although scans today have revealed no broken bones, United have not given any indication on when he is likely to be fit.
That means he is doubtful for Roma's visit on Wednesday and the Premier League clash with Arsenal on Sunday.
'Rio went for a scan on Monday and we can confirm that he has not suffered any break,' said a short club statement.
Ferguson has used Pique sparingly this season but has been hugely impressed by the 21-year-old Catalan in two recent appearances.
Pique steadied the ship when he came on for Ferdinand during the 2-2 draw against Middlesbrough.
He was also hugely impressive standing in for the England defender against Bolton last month when he came up against Kevin Davies, one of the most physical strikers in the Premier League, and emerged on top.
Ferguson said: 'Pique came on and did brilliantly [against Middlesbrough]. He was marvellous. The lad's a terrific player and I think that actually helped us.
'We've got great confidence in the lad and he's come through very well.'
Ferguson's side are already missing Nemanja Vidic, who has been sidelined for three weeks with a knee injury, and keeper Edwin van der Sar admitted the Serbian's absence caused problems during the 2-2 draw at the Riverside.
Van der Sar said: 'Of course we miss him, he is a very important player for us.
'It is no coincidence that with Vidic absent we had some problems but the players who came in did okay.'
John O'Shea had initially replaced Vidic but with Middlesbrough causing United problems, Ferguson shifted Wes Brown to centre-back and is likely to play him and Pique together against Roma.
United should still be confident of seeing off Roma, especially with their 2-0 advantage from the away leg, but Arsenal on Sunday will be a different proposition especially now the tension has been ratcheted up.