Thornton is expected to be called up from Triple-A Syracuse to pitch in Sunday's game against the Red Sox, Will Sammon of The Athletic reports.
Thornton will likely start or serve as a bulk reliever in Sunday's first-half finale, but the Mets haven't revealed their plans for the 24-year-old just yet. The southpaw has previously made two starts in the majors this season, giving up five earned runs while striking out 10 batters and walking three across 10.1 innings. Although he hasn't yet been able to claim a regular spot in the New York rotation, that could change within the next couple of weeks, depending on what moves the Mets make ahead of the trade deadline.