Hamels left Friday's game against the Reds in the second inning with an apparent left oblique injury, Jordan Bastian of MLB.com reports.
He missed time with an oblique injury in 2017, but that was to his right side. Mike Montgomery replaced Hamels, who was charged with one earned run on two hits and a walk while getting just three outs (one strikeout). Tyler Chatwood would likely step into the rotation in the short term if Hamels has to miss his next start.