"We rushed Fabio back a little bit, but given the situation we find ourselves in sometimes you have to do that," admitted the boss. "Rafa's only trained for a few days but he will be involved on Sunday."
Sir Alex also confirmed Wes Brown and Nemanja Vidic should both be available for the home game against Wigan on 30 December, and that the Reds' medical team are working to get one of the centre-backs fit for this weekend.
"We're trying to get one of them fit for Sunday, but we'll have to see," added Sir Alex. "The young boy [Ritchie] De Laet did okay in the last game at Fulham until we lost the first goal.
"The power and the strength of [Bobby] Zamora made things difficult for us and we looked fragile from then on. It's understandable in a way - you can get away with playing midfielders at centre-back once or twice, but it proved to be very difficult for us at Fulham."
The United boss is expecting an equally tough game against an improving Tigers side, saying: "Hull will be encouraged by our injury problems, and I'm sure they'll have a go at us.
"We have to make sure we are better attacking-wise than we were at Fulham. We had quite a bit of possession, but didn't make a lot of chances. We have to improve the imagination of our play on Sunday."