Rasmussen was optioned to Triple-A Durham on Sunday, Steve Carney of Sports Radio 620 WDAE reports.
Rasmussen was called up by the Rays on Saturday, and he struck out four in 1.2 perfect innings in Saturday's matchup against Seattle. He'll now head back to the minors as part of a transaction that's expected to make room for shortstop Wander Franco on the active roster.