Houser will undergo an MRI on his right arm Wednesday, Alex Pavlovic of NBC Sports Bay Area reports.
Houser was pulled from his start in the second inning due to arm tightness, and the results of his MRI will help determine whether he needs to spend time on the injured list. An IL stint for Houser would be a crucial blow to a Giants rotation that already lost Carson Whisenhunt on Monday to a UCL tear.