Diouf spent last season on loan at Blackburn but after a stunning hat-trick on his Carling Cup debut he managed just three goals for the rest of the campaign.
The 23-year-old went on United's pre-season tour of America, but Sir Alex Ferguson is prepared to cash in on the striker they paid Molde £3.75m for in 2009.
Blackpool boss Ian Holloway is interested in making a move for Diouf, but will not be able to match United's asking price.
Blackburn, Everton and Fulham are said to be monitoring the situation.
Source: Daily Mail