CHICAGO -- Chicago Cubs pitcher Alec Mills left Saturday's game against the Boston Red Sox due to lower back pain after throwing just seven pitches.
The Cubs said the right-hander is undergoing further evaluation.
The 30-year-old Mills (0-1, 9.87 ERA) struck out Jarren Duran and left after allowing a double to Rafael Devers.
Mark Leiter Jr. came in and struck out J.D. Martinez and got Xander Bogaerts to fly out, ending the inning.
Mills was activated June 7 from the 60-day injured list for a right quadriceps strain.