Santos was handed an 80-game suspension Tuesday after testing positive for Stanozolol, Mark Feinsand of MLB.com reports.
Santos appeared in three games after being called up to the majors in late June, allowing six runs (five earned) on five hits and two walks while fanning three. He was a candidate to potentially rejoin the Giants' bullpen later this season, but that appears extremely unlikely now, as he'll be ineligible to pitch at any level during San Francisco's next 80 games.