Middleton missed Sunday's game against the Utah Jazz with what the team initially believed was a non-COVID illness, before he entered the NBA's health and safety protocols ahead of Tuesday's game.
"We thought he just had a head cold or some type of non-COVID illness," Budenholzer said. "And then, [he] didn't feel good again the next day. Got tested and has come back positive."
A player who tests positive has to sit out for a minimum of 10 days, which could knock Middleton out for potentially the next six games through next Friday's matchup on the road against the Boston Celtics.
Middleton's absence is the latest blow to an already depleted Bucks roster. Entering Tuesday's game, only seven players had appeared in all seven of the team's games, including two-way guard Justin Robinson. Milwaukee had already been missing two starters -- Jrue Holiday (left ankle sprain) and Brook Lopez (back soreness) -- from opening night. Donte Divincenzo, their projected starting shooting guard, has not played since he injured his left ankle during the playoffs last year.
Holiday is on track to be the first to return among the group. He returned to practice recently, but after an abbreviated offseason following the NBA Finals and playing for Team USA in the Olympics, the team will be cautious with his return from injury.
"We've been very, very fortunate, it feels like, for my three years here in Milwaukee to be very, very healthy," Budenholzer said. "Yeah it's a challenge to figure out who's available, to get the best groupings out there and how we can get through a game. And not really wear down the guys that are healthy."