The Brewers' No. 2 prospect lasted just 3 1/3 innings -- coming out in the middle of an at-bat -- in Class A Advanced Brevard County's 2-1 loss to Daytona.
Brewers assistant general manager Gord Ash told MLB.com that Bradley was removed with a mild groin strain.
On the night, Bradley (4-3) surrendered two runs on three hits and two walks. The outing marks the first time that he failed to pitch at least five innings, as well as the first time that he did not record a strikeout.
The 21-year-old left-hander scuffled in the first inning, allowing four of the first five batters he faced to reach base. Arismendy Alcantara led off the game with a single, while Ronald Torreyes followed with a walk. After a popout by Rubi Silva, Greg Rohan drew a free pass and Nelson Perez delivered a two-run single.
Bradley went on to retire the next eight batters he faced before Perez again singled in the fourth. He then threw one pitch to John Andreoli, but was replaced by reliever Brian Garman in the middle of the at-bat.
"It was weird, he didn't even limp or anything," said Robbie Aaron, the Daytona Cubs' director of broadcasting and media relations. "We didn't know if he was injured or something happened. The coaching staff and trainer came out. We didn't know if he was hurt, but he didn't look like he was in pain."
Drafted with the 15th overall pick in June, Bradley has posted a 3.53 ERA through 43 1/3 innings with the Manatees. He has fanned 36 while walking 14.