PITTSBURGH -- Right-hander Mitch Keller, the Pirates' top prospect according to MLB Pipeline, is moving closer to the big leagues.
Keller, 22, will make his next start for Triple-A Indianapolis, the club announced. Keller went 9-2 with a 2.72 ERA and 1.12 WHIP in 14 starts for Double-A Altoona this season. Keller is MLB Pipeline's 13th-ranked prospect in all of baseball.
Keller is not on the Pirates' 40-man roster, and while it's possible he could be called up in September, he likely won't make his Major League debut until next season. Keller was not invited to big league camp this spring, but he gave the Pirates a preview of his potential while striking out three over two scoreless innings during a Spring Training game against the Red Sox.

"I'm not trying to get too far ahead. But it's close," Keller said on March 18. "Just talking with people, I'm right there, so I just got to hone in my craft and just get everything a little bit better than it already is and be more consistent. So that's really what I'm looking for."
Keller, the Pirates' second-round Draft pick in 2014, is viewed as an advanced, polished young pitcher. After making six Double-A starts last season, he held opponents to a .208 average while striking out 76 batters in 86 innings for Altoona this year. He has been particularly effective of late, going 4-0 with a 1.11 ERA over his last five outings -- all quality starts.
If the Pirates were looking for proof that Keller was ready for the next step, he provided it in his last Double-A start. Keller allowed only one hit and two walks while striking out six over eight scoreless innings against Harrisburg. General manager Neal Huntington recently said Keller's changeup has improved. That pitch had been considered the missing link for Keller, who throws a fastball in the mid-to-upper 90s, with a swing-and-miss curveball.
"To see him grow and develop the way he has, our staff's done a great job and Mitch deserves a ton of credit, too," Huntington said on Sunday at PNC Park. "We've still got some growth to go, but we believe he can be a really good Major League starting pitcher."