AC Milan captain Paolo Maldini is all but out of Wednesday's Champions League semi-final second leg match against Manchester United at San Siro due to injury.

The 38-year-old defender, who is aiming to reach the final of Europe's top club competition for the eighth time, is struggling to shake off a knee injury he picked up in Milan's 3-2 first leg defeat at Old Trafford last week.

"There are very slim chances of having him (fit for the match)...I will decide on him in the evening," coach Carlo Ancelotti told the Gazzetta dello Sport Web site.

Aside from Maldini, Ancelotti has a full-strength team at his disposal. If his captain fails to recover, Ancelotti is expected to field Daniele Bonera in his place.

While Maldini stands a slim chance of starting the game, United captain Gary Neville has already been ruled out by an ankle injury.

The Premier League leaders' injury problems in defence could be eased, however, by the return of Rio Ferdinand and Nemanja Vidic.

The pair missed the first leg due to a groin strain and broken collar bone respectively, but flew out to Milan after coming through late fitness tests.

United manager Alex Ferguson will hope at least one of them can start, allowing him to move Argentine international Gabriel Heinze from the centre of the defence into his favoured left-back position.

Louis Saha could also give United an extra attacking option on the bench after recovering from a hamstring injury.

The winners of the tie will meet Liverpool in the May 23 final in Athens after beating Chelsea on penalties in the other semi-final tie which ended 1-1 on aggregate on Tuesday.