Senegal’s Diouf (Photo: Reuters)
The 30-year-old Senegal international has been without a club since he was released by Blackburn at the end of last season.
A two-time African Footballer of the Year, Diouf was a £10 million arrival at Anfield in 2002 after playing a starring role in Senegal's successful World Cup campaign that summer.
Diouf has also played for Sunderland in the Premier League and helped Rangers to the Scottish Premier League title during a loan spell north of the border last term.
His arrival at the Keepmoat Stadium will go some way to addressing the striker problems testing boss Dean Saunders. Goalscorer James Hayter was the only established centre-forward in the squad for the 1-1 draw with Coventry on Saturday.