Duffey was optioned to Triple-A Rochester on Sunday, Brandon Warne of The Athletic Minnesota reports.
Duffey gave up one run over three innings during Sunday's 8-2 loss to the Reds. Since being recalled from Rochester on April 24, Duffey has thrown 5.1 innings over three games, during which he's surrendered four home runs. The Twins plan on announcing a corresponding move before Monday's game against the Blue Jays.