Diouf has been scoring goals in the Bundesliga for Hannover, but is set to leave the club in the summer once his contract expires after talks over a new deal hit deadlock.
Diouf struggled during his time at Old Trafford, but has scored consistently in Germany since his departure.
The Senegal international will demand a signing on fee as no transfer fee will be paid to his club, and Stoke appear firmly in the running for his signature.
Cardiff City also remain interested, but a move will be dependent as to whether the club can preserve their Premier League status.
Mark Hughes is hoping to add attacking reinforcements in the summer, and has been impressed with the 26-year-old who has managed eight league goals in 19 appearances this season.
Ole Gunnar Solskjaer will fancy his chances of persuading Diouf to join Cardiff should they avoid the drop however, as both share an affection with Norwegian club Molde.
Solskjaer enjoyed a successful spell as manager, while Diouf fired 33 goals in 75 appearances before leaving the club in the summer of 2012.