Diouf, who arrived at the HDI Arena from Manchester United for an undisclosed fee in January 2012, is out of contract at the end of the season, when he could depart on a free transfer.
And Dufner believes the Senegalese striker's days at Hannover are numbered.
"The signals are clear that he will go," he told Bild.
It is as yet unclear whether Hannover will look to cash in on the forward in January or hang onto him until the end of the current campaign, but news of his potential availability will have pricked the ears of Premier League club Stoke City, who were heavily linked with Diouf in the close-season.
The 26-year-old has scored five goals in 12 Bundesliga appearances this term.
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