ST. LOUIS -- Right-hander Jon Gray, the Rockies' top pick in the 2013 Draft and their top-ranked pitching prospect and No. 2 prospect overall, according to MLB.com, will make his Major League debut on Tuesday night against the Mariners at Coors Field, a source told MLB.com on Sunday night.
Gray, 23, chosen third overall out of Oklahoma, has gone 6-6 with a 4.33 ERA in 21 games, including 21 starts, at Triple-A Albuquerque. He started slowly, but since May 2 he is 6-3 with a 3.17 ERA, 93 strikeouts and 33 walks over 17 outings.
Listed at 6-foot-4, Gray is a big pitcher with a heavy fastball, and was clocked at faster than 100 mph on many occasions in college. As a pro he can reach the upper 90s when necessary but tends to work in the 93-95-mph range.
As the Rockies' struggles with starting pitching deepened, calls to bring up Gray grew loud. Gray seemed to be knocking at the door in late May and early June. On May 31 he threw seven scoreless innings with four hits in a no-decision against Omaha. Two starts later he held Tacoma to two runs on four hits with four strikeouts in another no-decision. From there the strikeouts began to climb.
However, noting that Gray was consistently needing 100 pitches to complete five or six innings, the Rockies kept him at Albuquerque to work on his efficiency. Gaining more consistency with his slider and changeup, and handling such finer points as fielding and controlling the running game were emphasized.
Gray, with whom the Rockies are being careful because it is his second full professional season, has gone just five innings in each of his last three starts. In the most recent outing, a victory over Salt Lake, he needed just 70 pitches in striking out eight against three hits and one walk.
Coming up now could give Gray a chance to gain his Major League footing through five starts before the rosters expand on Sept. 1 and teams out of the playoff race look at games as tryouts for future opportunity.
Now the team's top two pitching prospects will have a chance to work on consecutive turns.
Righty Eddie Butler, who was rushed to the Majors last year and at the beginning of this season before catching his breath during a trip to Albuquerque, has turned in solid work in two official starts, plus one that was rained out before the game became official. He will start against the Mariners on Monday night at Coors.
Inserting Gray into the Tuesday slot allows the Rockies to give an extra day of rest to lefty Chris Rusin, who will start Wednesday's series finale with the Mariners.
The spot for Gray opened when righty Kyle Kendrick suffered inflammation in his right shoulder on Friday night against the Cardinals, had to leave the game and was placed on the 15-day disabled list.
Thomas Harding is a reporter for MLB.com. Follow him on Twitter @harding_at_mlb, and like his Facebook page. This story was not subject to the approval of Major League Baseball or its clubs.