Ferguson believes his replacement, Jonny Evans, stands comparison with the very best.
"I must admit my heart sank a little when I learned just how long Nemanja Vidic was going to be out," the Scot said.
"Jonny came to us from Belfast when he was 12 or 13, always exceptionally talented but gangly with physical issues growing up.
"We had him out on loan with Antwerp and Sunderland and now we are seeing the value of nurturing him.
"There is no doubt he has been helped playing alongside the experience of Rio and he is now arguably the best defender in the country."