The team announced it as a "lower body injury" and said Dekker is day-to-day, according to the Wisconsin State Journal.
The WSJ reports that Dekker fell to the ground while driving to the basket, then hopped on his other foot into the locker room and didn't return.
Dekker was selected to the preseason All-Big Ten team by the media, and Wisconsin senior center Frank Kaminsky was chosen as the preseason Big Ten Player of the Year.
Last season, Dekker averaged 12.4 points, 6.1 rebounds and 1.4 assists while shooting 46.9 percent from the floor. He started all 38 games for the Badgers, who went to the Final Four and finished 30-8.
Wisconsin was chosen No. 4 in the preseason Coaches Poll. The Badgers first game is on Nov. 14 against Northern Kentucky.
- Molly Geary