News that winger Nani is set to complete a remarkable recovery from a badly gashed shin - by playing just four days after he had been ruled out until next month - was almost immediately overshadowed by the bleak update on Vidic.
The Serbia defender only returned from suspension in Saturday's FA Cup quarter-final against Arsenal, but picked up a knock in the 2-0 win and was unable to train on Monday.
On the ball: Nani (right) could return sooner than expected for Manchester United
Calf injury: United skipper Nemanja Vidic
United are keen to have Vidic available for Saturday's Barclays Premier League game against Bolton to combat the physical presence of Kevin Davies.
'He was getting treatment,' said Sir Alex Ferguson. 'He's tough enough but couldn't train in the morning.'
With Rio Ferdinand and Jonny Evans out, it means the United manager might have to rely on the central defensive partnership of Chris Smalling and Wes Brown which proved so vulnerable against Liverpool nine days ago.
Although Smalling has made outstanding progress this season and was arguably the best player in the goalless first leg in Marseille, the 21-year-old looked less assured at Anfield as United lost 3-1.
United will want to avoid conceding an away goal against the French champions as they seek the win which would put them into the quarter-finals.
At least there was better news on Nani. Ferguson admitted he did not expect to see the forward back in action before April after hitting out at the 'disgraceful' tackle from Liverpool's Jamie Carragher that cut the Portugal star's shin.
However, a successful attempt to stitch the wound appears to have speeded up the healing process dramatically.
Swift recovery: Nani was not expected back in action until next week after he injured his leg at Liverpool
Ferguson must now decide whether to name Nani in his starting line-up, with Antonio Valencia also available after coming through 45 minutes against Arsenal.
The United boss also confirmed Michael Carrick is expected to play after recovering from calf and groin injuries. He said: 'Nani's got a good chance. He trained on Sunday alongwith Michael Carrick, which is a better situation than we had at the weekend. Both will be involved tomorrow.
'It was a fantastic bonus for us to get 45 minutes from Antonio considering he's been out for such a long time.'
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Explore more:People: Alex Ferguson, Kevin Davies, Jamie Carragher, Nemanja Vidic, Rio Ferdinand, Wes Brown, Antonio Valencia, Michael Carrick, Nani Places: Liverpool, Portugal