Middleton, averaging 20.4 points, was ruled out Sunday after scoring 21 points the previous night in a win over Miami. The two-time All-Star is missing his fourth game this season.
"We feel like if we can kind of get on top of it this 24, 48 hours, I think he'll be in a great place heading into the week of prep and playoffs," coach Mike Budenholzer said.
The Bucks began the day a game behind Brooklyn for the No. 2 seed in the Eastern Conference playoffs. They needed a win over the Bulls plus a loss by the Nets to the Cleveland Cavaliers to clinch the second seed. Otherwise, they would finish third in the East.
Milwaukee had won three straight and eight of nine entering Sunday's matchup.
The Bulls were missing their two best players with Zach LaVine sitting out his second consecutive game because of tendinitis in his right knee and Nikola Vucevic held out because of nagging hip issues. Daniel Theis (sprained right hip), Tomas Satoransky (sprained left ankle) and Troy Brown Jr. (sprained left ankle) also were unavailable. Chicago was eliminated from contention for the play-in tournament Friday when Washington beat Cleveland.