Estrada was optioned to Triple-A Iowa on Saturday, Meghan Montemurro of the Chicago Tribune reports.
Estrada is a popular speculative play for saves in draft-and-hold leagues, but it seemed likely he would open the year in the minors. He gave up one run with four strikeouts in four innings this spring after registering nine saves across the three highest levels of the minors last season en route to making his big-league debut.