A team that let in 22 goals on their way to winning the title in 2009 with Ferdinand and Nemanja Vidic at the heart of their defence, has already leaked nine in six games with Jonny Evans alongside Vidic.
But Ferguson insisted he has yet to make a final decision if Ferdinand is to face Valencia, saying: "Rio has had plenty of training and a couple of reserve games. He had a game against Rangers and I think he probably needs another game or two.
"That goes without saying considering he's been out for five months, that's why I didn't risk him against Bolton. The important thing is that he's coming back and we can look forward to having him back."