"Obviously we have some injury problems and we won't know until tomorrow for O'Shea.
"He did a little light session on his own, not with the other players. Jonny Evans wasn't able to train."
Ferguson jokingly said that his defensive crisis had left him panicking ahead of Tuesday's Champions League clash.
His selection headache is even more severe than first thought with teenage Brazilian right-back Rafael da Silva the latest player to be ruled out with an ankle injury.
Veteran Gary Neville and Wes Brown are already on the treatment table while Nemanja Vidic is suspended and both Jonny Evans and John O'Shea are rated as highly doubtful for the game.
Ferguson revealed that Rafael's twin brother Fabio could switch from his usual left-back slot to fill in the gap on the right.
"The options are: panic. I think I can play Dimitar (Berbatov) as sweeper," joked Fergie.
"I hope one of them (Evans and O'Shea) will make it. O'Shea might, then we have the problem at right-back."
"These these are the major doubts but everyone else is fit and travelled."
Ferguson agreed that the match could boil down to a shoot-out between two of the best players in Europe, Inter's Zlatan Ibrahimovic and United's Cristiano Ronaldo.
"Their star player without any question is Ibrahimovic. He's had a fantastic season and is getting all the praise he deserves," he added.
"I've watched him for many years and he has developed. He's at that age where you expect a bit of maturity and that is what we are seeing now.
"Everything has already been said about Cristiano, he's a fantastic player and I hope my players have a better night tomorrow than Inter."