Astros prospect right-hander Mark Appel had his best start of the season on Thursday and now Evan Drellich of the Houston Chronicle reports that he’s set to be promoted to Double-A Corpus Christi.

When the Astros chose Appel first overall in last June’s First-Year Player Draft, many believed that he was on the fast track to the major leagues. Of course, it hasn’t worked out that way. After a solid showing in his pro debut last season, the 23-year-old has struggled to the tune of a 9.74 ERA over 12 starts this season with High-A Lancaster. He got a late start this spring following an appendectomy in late January, but the Astros sent him to a full-season affiliate anyway and he had some trouble adjusting to the organization’s piggyback pitching rotation. He has also missed some time with right wrist and thumb issues.