The England captain has been out of action for the last two months while he recovered from the knee ligament injury which ruled him out of the World Cup.
Ferguson revealed on July 25 that the 31-year-old would not be back in action for six weeks, but that estimate now looks to be well wide of the mark.
The Sunday People has Ferguson as saying: "Rio is nowhere near, no. He's doing little bits of jogging and things like that but I think he's a month away.
"We always anticipated it would take time. It's a knee ligament and, although it wasn't what you'd call a serious one, it was a hard one. You have to take time with knee ligaments."
Sir added: "Rio has had a bad 12 months and we hope it gets better for him.
"You hope the break over the summer with missing the World Cup will help him.
"The back injury seemed to sort itself out as the season went on, then he had the groin injury.
"He's had a succession of these things and you don't want to see that when a player is in his 30s."