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Ferdinand was a surprise name in the England squad selected by Roy Hodgson this week after previously being overlooked by the national team manager.
But Ferguson says concerns about Ferdinand's fitness may mean that he withdraws himself from the squad.
"I think he has to make sure he is OK in terms of the number of games he has played. That's a factor," said Ferguson. "Rio is considering that and we will see what the outcome of that is.
"Obviously, I was as surprised as anyone when I heard that (Ferdinand had been called up).
"I need to speak to our doctor. We prepare Rio in certain ways, he has certain treatments to go through, certain procedures, which have given him fantastic performance levels when he has played for us. We have to consider that.
"We have been doing it for two years and it works. We have a detailed programmes, give him the treatment he needs for the various complaints he has had in terms of his back, groin, things like that.
"So far it has worked very well. We will have to look at all these things before Rio decides."
Ferguson also hit back at allegations from Rafael Benitez that he snubbed a pre-match handshake before last weekend's 2-2 draw with Chelsea in the FA Cup.
A thrilling tie at Old Trafford was almost eclipsed by the claims of Chelsea's interim manager that Ferguson had refused to shake his hand before kick-off, prompting Benitez to walk onto the field and ignore his counterpart at the final whistle.
"Absolute nonsense," Ferguson said. "Why wouldn't I shake his hand? Think about it.
"I never saw him. I was signing autographs at the front, chatting with that young kid who always wants to shake my hand before the game because he says it brings us luck! I moved across and I never saw him.
"I don't know why he said that. If he wanted to shake my hand, he could have stood in front of me. I've absolutely no idea why he said that. It's nonsense."
Ferguson has also analysed the state of English football in the wake of the Premier League clubs' poor showing in this season's Champions League.
No English side have reached the quarter-finals after United's controversial exit to Real Madrid and Arsenal's defeat over two legs by Bayern Munich. Chelsea and Manchester City had earlier failed to make the knock-out stages.
"You can't put us all in one basket," said Ferguson. "I think our performance against Real Madrid was outstanding and we could have been in the last eight.
"It is also cyclical. You look at the performance levels of (Borussia) Dortmund and Bayern Munich and they have improved this year.
"Spain has been like that for a few years now, but a few years ago English teams were in the semi-finals, the final regularly. It's a bit of a cycle in terms of German teams progressing.
"I don't think you can put us all in one basket in terms of deterioration. I don't think that at all."
