Premier League clubs looking for a new keeper have been told it will take £4million to land World Cup hopeful Foster, whose relationship with Sir Alex Ferguson soured after a dressing-room row following the home game against Sunderland in October.
Out of favour: United keeper Ben Foster
Foster's impending departure signals the start of a major shake-up at Old Trafford, prompted by last weekend's FA Cup flop against Leeds United.
With Ferguson no longer able to shop at the top end of the market, he has targeted West Ham's £6m midfielder Valon Behrami to add creativity and is looking at Brazilian defender Joao Miranda of Sao Paulo as a long-term replacement for Nemanja Vidic.
Anderson and Nani will also be allowed to go at the right price and a summer move for Real Madrid striker Karim Benzema cannot be ruled out if Ferguson can find a buyer for Dimitar Berbatov.
The decision to sell 26-year-old Foster marks a huge decline in fortunes for someone hailed as the future of English goalkeeping by Ferguson earlier this season.
But a series of mistakes culminating in a couple of blunders in the 2-2 draw against Sunderland have left the United manager convinced Foster has to move clubs to restore his confidence. He has only played for United in one game since - a meaningless Champions League tie against Besiktas.
Foster's departure is likely to be hastened by Van der Sar's return to the club's training ground in Carrington next week. His wife, Annemarie, was released from Leiden University Hospital on Friday night, two weeks after she suffered a stroke.
Van der Sar, who last played for United against Everton on November 21, said: 'Yes, I'm more or less ready to step it up and resume training with Manchester United. In the past week I have trained with my old club, Ajax.'
Meanwhile, Ferguson has turned his attentions to 24-year-old Swiss international Behrami and West Ham's financial situation means they are unlikely to be able to resist a bid.
Ferguson will be allowed to sign players for United this year but will have a tight budget with the club £700m in debt under the ownership of the Glazer family.
Birmingham 1 Man United 1: Dann own goal rescues point for 10-man United Cristiano Ronaldo's stunning strike against Porto voted Manchester United's goal of the decadePATRICK COLLINS: Is it time for Ferguson to ride into the sunset?