The Rays designated Guerra for assignment Wednesday.
Guerra's contract was selected by the Rays on Saturday.
Tampa Bay outrighted Guerra to Triple-A Durham on Wednesday, Marc Topkin of the Tampa Bay Times reports.
Tampa Bay designated Guerra for assignment Sunday, Ryan Bass of Bally Sports Sun reports.
Guerra will operate as the Rays' opening pitcher for Sunday's matchup with the Yankees, Ryan Bass of Bally Sports Sun reports.
Guerra will serve as the Rays' opening pitcher for Tuesday's game against the Pirates, Marc Topkin of the Tampa Bay Times reports.
The Rays will add Guerra to their 26-man roster Sunday, Marc Topkin of the Tampa Bay Times reports.
Guerra was traded from the Brewers to the Rays on Saturday in exchange for a player to be named later or cash considerations.
The Brewers designated Guerra for assignment Monday.
Guerra, per Adam McCalvy of MLB.com, secured a spot on the Brewers' Opening Day roster.