Duffey was sent down to Triple-A Rochester on Thursday, Rhett Bollinger of MLB.com reports.
Duffey was lit up his last time out, yielding six runs over three innings in a losing effort Wednesday, as he saw his ERA rise to 6.24 on the season. The 25-year-old will try to figure out what's been going wrong back in the minors, while Andrew Albers will join the major league roster in a corresponding move.