The 40-year-old Dutch keeper's retirement has been on the cards for some time and United have been preparing to have to fill some big boots by bringing in Dane Anders Lindegaard who will be registered with the club in early January.
"We're planning for it to be possibly Edwin's last season," Ferguson told a news conference.
Asked if there might be a coaching role for Van der Sar, the manager replied: "He'll be someone of interest in terms of his knowledge and standing in the game, but we haven't discussed that yet."
Moments of brilliance have been peppered with the odd blunder like the one in October's 2-2 draw with West Bromwich Albion where he dropped a simple catch in a mistake Ferguson said was "inexplicable" but one he would make "the only time in his life".
His cool head at the times when it really counts, such as when he saved Nicolas Anelka's final penalty in the shootout against Chelsea in the 2007/08 Champions League final, are what United will miss.
"He is training with us now and that is important," Ferguson said of Lindegaard, who has joined from Denmark's Aalesund for 3.5 million pounds according to British media.
