Ferdinand was selected by Roy Hodgson for this month's World Cup qualifiers with San Marino and Montenegro, the first time he has been called up by the current England boss since he took charge just before Euro 2012.
The move caught Ferguson by surprise given Ferdinand's long-standing back and fitness issues and the Scot was not convinced a return to the international set-up, at the age of 34, was right for his experienced centre-half.
Ferdinand's current five-year deal expires at the end of the current campaign and the United manager said: "I was as surprised as anyone when I heard.
"I need to speak to the (United) doctor because we prepare Rio Ferdinand in a certain way and there are certain treatments he has to go through.
"He has to make sure he is going to be OK in terms of the number of games he plays.
"We have been doing that for two years and it has worked. We have to look at all these things before Rio decides (if he joins up)."
If Ferdinand did not report it would be more than a minor embarrassment for England boss Hodgson given his climbdown from previous statements that he has "moved on" from the Manchester United defender.
"The procedures have been the same all season which has given him fantastic performance levels when he's playing for us," said Ferguson.
"We have to consider that and Rio is considering that. And we'll see what the outcome of that is."