Littell will serve as an opener Thursday against the Diamondbacks, Marc Topkin of the Tampa Bay Times reports.
Littell will take the mound first for Tampa Bay, with Yonny Chirinos slated to cover bulk relief innings. It will be the first opener assignment this season for Littell, who holds a 6.57 ERA and 11:5 K:BB over 12.1 innings covering 10 appearances between the Red Sox and Rays.