Manchester United goalkeeper Edwin van der Sar has signed a new one-year contract extension, tying him to the club until the end of the 2009 season. The 37-year-old had been considering retirement at the end of this season. "He is number one at the moment, but you can't guarantee players a position and say they'll definitely be in your team," said boss Sir Alex Ferguson. "Edwin will want to be number one next season but Ben Foster will be back and I am sure he will want to be too." England international Foster is currently sidelined after cruciate knee ligament surgery. There were suggestions Van der Sar could be handed a role on the Old Trafford backroom staff as goalkeeping coach Tony Coton is currently sidelined following a recent knee operation. But Ferguson stressed the Dutchman's new deal was "totally as a player".