Koss was diagnosed with a fractured left wrist Tuesday, John Shea of the San Francisco Chronicle reports.
Koss hasn't played at Triple-A Sacramento since May 23, and he's now facing an extended absence. The Giants haven't announced a return timeline for the 28-year-old infielder, though he may be a candidate to land on the 60-day IL at some point if the team needs to free up a 40-man roster spot.