O'Shea picked up a thigh injury during the Republic of Ireland's shattering World Cup exit in France last month that Ferguson initially felt was nothing more than a dead leg.
However, O'Shea has not played since. And while Rio Ferdinand and Jonny Evans are inching towards their returns from injury and Nemanja Vidic and Wes Brown have already made it back to the Red Devils first team, for O'Shea the delay goes on.
"There is no sign at all of recovery for John,'' said Ferguson. "It is his first injury at the club and he is a big loss because he is such a versatile player. We just want to get him back but it could be a couple of months yet.''
Ferguson revealed that when O'Shea got back from France, blood congealed in his muscle, raising the possibility of further problems. It consigned O'Shea to the sidelines at a time when his ability to play right across the back four would have been invaluable.
In his absence, the likes of Darren Fletcher and Michael Carrick have been forced to help out in defence, one of the major reasons why United lost twice in three games to put their Premier League title hopes in jeopardy.
The joint return of Vidic and Brown has coincided with a two-match winning run over Christmas that yielded eight goals, five of them coming against Wigan at Old Trafford on Wednesday night.
Vidic and Brown will continue to shoulder the burden for now but Ferguson is optimistic Evans will return to duty in the next ten days, with Ferdinand not too far behind after United finally got to the root of a back problem that has plagued the England defender for 18 months.
"Jonny has been involved in the football side for a few days,'' said Ferguson, who is celebrating his 68th birthday on Thursday. "He is doing well and should be back quicker, within the next 10 days or so.
"Rio is nowhere near that but the main thing is there is no recurrence of the back problem. That is what we have been waiting for. We wanted him to come through the test of running and turning. He is doing his programme in the gymnasium, which is good and at the moment it is looking very healthy.''