Bulls head coach Fred Hoiberg told K.C. Johnson of the Chicago Tribune that Dunn suffered an "open dislocation" and will be sidelined for a couple weeks.
Dunn was selected fifth overall in the 2016 draft, but his rookie season wasn't particularly memorable.
Appearing in 78 games for the Minnesota Timberwolves, Dunn averaged 3.8 points, 2.4 assists, 2.1 rebounds and 1.0 steals.
"My rookie season, there were a lot of ups and downs, basically like a roller coaster ride," Dunn said, according to CBS Chicago's Cody Westerlund. "Playing under Tom [Thibodeau], he helped me become a professional. He loves players that love to work. He made sure all his guys are always in the gym working hard, attacking every day, trying to improve each day."
Following one year in Minnesota, Dunn was shipped to the Bulls as a centerpiece of the blockbuster trade that helped the Timberwolves land Jimmy Butler.
Jerian Grant, who started 28 games for the Bulls last season, will be the primary candidate to fill in for Dunn.