The Premier League club have yet to finalise their move for the 26-year-old Hannover striker, who is out of contract this summer.
Diouf has already passed his medical with Stoke, but has yet to put pen-to-paper, and that has left the door open to other clubs to continue their chase.
When asked about Diouf's situation, Wolfsburg's general manager Klaus Allofs told kicker-Sportmagazin: "Everything that has not become a done deal in time is actually absolutely not checked off from our point of view."
Wolfsburg are looking at bringing in at least one striker this summer and have also been linked with the likes of Chelsea forward Romelu Lukaku, Real Madrid's Alvaro Morata and Hertha Berlin's Pierre-Michel Lasogga in recent weeks.
"We are looking at a handful of strikers at the moment," Allofs added.