Butto was diagnosed with a blood clot in his right arm and will undergo a procedure Friday to remove it, Alex Pavlovic of NBC Sports Bay Area reports.
Butto exited his appearance Wednesday alongside a trainer before landing on the injured list Thursday with right forearm fatigue. The Giants haven't announced a timeline for the 28-year-old's return, but he's now likely to spend far more time on the injured list than the 15-day minimum.