Gallen (hamstring) will undergo an MRI on Saturday, Jody Jackson of Bally Sports Arizona reports.
Gallen exited Friday's game against the Giants in the top of the third inning and was diagnosed with right hamstring tightness. His tests should help determine his status going forward. The right-hander had been charged with losses in three of his last four starts. It's not yet clear whether he'll be able to make his next turn through the rotation.