Drew Pomeranz was checked on by the trainer while working a scoreless eighth against the Pirates on Saturday.
The Cubs said after the game that it was lower back tightness for Pomeranz, who stayed in and finished the inning after the visit. Pomeranz has been terrific for the Cubs after being rejected by the Mariners, allowing only one unearned run (an automatic runner scoring in the 10th) over 18 1/3 innings in a setup role.