Yarbrough is expected to serve as the Rays' primary pitcher in Thursday's series opener against the Astros in relief of likely starter Ryne Stanek, Marc Topkin of the Tampa Bay Times reports.
Before confirming their plans for Thursday, the Rays will presumably monitor the bullpen's usage in Tuesday's game against the Nationals. If Stanek nor Yarbrough are used extensively, both pitchers should be available Thursday, with the latter covering the bulk of the innings. Stanek hasn't recorded more than six outs in any of his seven "starts" this season, while Yarbrough has covered between 3.1 and 5.1 innings the three times this month he has relieved either Stanek or Jonny Venters.