Injury blow: O'Shea is out for the rest of the season
The Republic of Ireland international has been sidelined since November after he was initially diagnosed with a dead leg following their World Cup 2010 qualifying play-off defeat against France.
Ferguson had expected the versatile stopper to return to his plans within days but the problem proved far more complicated and after undergoing a series of medical tests the United chief revealed O'Shea is certain to sit out the remainder of the campaign.
'He's got a terrible injury at the moment,' said Ferguson.
'The problem is that the blood clot became all knotted and when it gets knotted you get calcification, so therefore it's a long process.
'He's probably out for the season now. It's a bad blow for the boy and for the team because he can play anywhere.'
With no return date pencilled in for fellow defender Rio Ferdinand and both Nemanja Vidic and Jonny Evans suffering injury problems earlier this term, Ferguson may look to bring in reinforcements before the transfer window slams shut on February 1.
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