Fleming will be called up from the Rays' alternate training site to start Sunday's game against Toronto, Marc Topkin of the Tampa Bay Times reports.
The outing will be Fleming's major-league debut. It's not clear that he'll have the chance to stick in the rotation long-term even if he pitches well, however, as Charlie Morton appears to be working his way back from a shoulder issue. The 24-year-old lefty threw 148.2 innings in the two highest levels of the minors last season, posting a 3.57 ERA and a 4.4 percent walk rate but striking out just 17.7 percent of opposing batters.