Dunn hurt his finger after trying to contest a dunk from Bucks shooting guard Sterling Brown.
Dunn will see a specialist on Saturday for further evaluation, and his wound will have to heal after stitches are applied. Hoiberg said Dunn is expected to miss at least two weeks.
The Bulls open the regular season Oct. 19 against theToronto Raptors.
Brown dunks over two defenders
Sterling Brown throws down a one-handed jam over two Bulls defenders and draws a foul. Kris Dunn gets hurt on the play.