The Giants placed Small (oblique) on the 60-day injured list Thursday.
Small will be sidelined for several weeks after being diagnosed with a moderate right oblique strain, Maria I. Guardado of MLB.com reports.
Small has allowed one run on five hits and a walk with six strikeouts over 3.2 innings across two Cactus League games.
The Brewers optioned Small to Triple-A Nashville on Friday.
Small was recalled from Triple-A Nashville on Wednesday.
Small was optioned Triple-A Nashville on Saturday.
Milwaukee recalled Small from Triple-A Nashville on Friday.
Manager Craig Counsell said Wednesday that Small is competing for a spot in the Brewers' Opening Day bullpen as a long reliever, Todd Rosiak of the Milwaukee Journal Sentinel reports.
Small was optioned to Triple-A Nashville on Wednesday.
Small allowed three runs on four hits and four walks while striking out three in 3.2 innings in a 7-6 victory Tuesday against Minnesota. He did not factor into the decision.