Lopez exited Sunday's start against the Twins with the athletic trainer after retiring two of the seven batters he faced, James Fegan of The Athletic reports.
The 26-year-old struggled with his control and his velocity was down a bit; he delivered only 19 of his 38 pitches for strikes as he allowed four runs on three hits and two walks. Lopez was seen wincing after delivering his final pitch, but the specifics of the situation remain unclear.