Yarbrough was optioned to Triple-A Durham on Saturday, Neil Solondz of the Rays Radio Network reports.
Yarbrough struggled mightily during Friday's start against the Red Sox, giving up five runs on eight hits and two walks while striking out three in 3.1 innings to take his eighth loss of the season. Although he had been relatively productive over his two appearances ahead of Friday's start, he'll still be sent to the minors to make room for Garrett Cleavinger on the active roster. The team hasn't announced who will take Yarbrough's spot in the rotation, but it's possible that the club rolls with a four-man rotation for the time being since the Rays have two days off next week.