The 25-year-old is set to move for a fee of around 12 million pounds ($21.72 million) but it is unlikely to be finalised until United manager Alex Ferguson returns
United's next game is against third division Northampton Town on Sunday but Saha is ineligible.
Fulham moved quickly to replace Saha by signing United States international Brian McBride from Columbus Crew on a two-and-a-half year deal on Tuesday.