Nani left the pitch on a stretcher and could be sidelined for up to three weeks after requiring stitches to repair a deep leg wound.
Ferguson did not immediately comment on the first-half incident at Anfield, for which Carragher was only booked, due to a self-imposed media blackout, but has now broken his silence.
"It was a disgraceful tackle, we know that, but you move on," said Ferguson. "It is difficult to say exactly when he will be ready to return but we won't get him back for Bolton next Saturday."
He is definitely out of Saturday's FA Cup quarter-final against Arsenal, as well as Tuesday's match with Marseille.
"We've managed to stitch it, which is great news. What we're guarding against, of course, is infection," Ferguson added.
"The swelling has gone down a great deal, which is good news - but to give you a date for when he is coming back is very difficult to say.
"On the plus side, we've got a two-week international break from next Saturday, so he'll be ready for the return after that obviously, that's for sure."
Many observers felt Carragher's challenge warranted a straight red card and the Liverpool defender made a personal apology to Nani immediately after the game.
The 24-year-old winger will be one of ten senior players missing for United's FA Cup quarter-final clash with Arsenal on Saturday afternoon.