The Rockies hope a patient and at times painful development period begins to pay off on Saturday night, when right-handed pitcher Ryan Castellani makes his Major League debut with a start against the Mariners at T-Mobile Park in Seattle. The matchup can be seen live on MLB.TV at 7:10 p.m. MT.

A second-round pick out of Phoenix's Brophy Prep High School in 2014, Castellani, 24, will join the rotation in place of righty Chi Chi González, who was placed on the injured list Friday with right biceps tendinitis. He's ranked by MLB Pipeline as the Rockies' No. 18 prospect.

Castellani spent a full season at each Class A level and two full seasons in Double-A. Last year, he lost most of the Triple-A Albuquerque season because of a right elbow problem that required a cleanup surgery. But Castellani found success in the 2019 Arizona Fall League (1-0, 2.16 ERA, 20 strikeouts and seven walks in 16 2/3 innings), and followed that up with strong showings in Spring Training and Summer Camp.

Castellani, who brings a solid fastball, a couple of breaking pitches and a changeup, was on the season-opening road trip as part of the taxi squad, and he has built up his pitch count in intrasquad games at the Rockies’ alternate training site.

“High School pitcher -- a lot of times that takes a little time to fully get grounded, to understand how you get your outs,” Rockies manager Bud Black said. “With Ryan, a lot of it was his delivery, finding his correct arm slot that worked for him, and the mix of pitches -- what type of pitches that were best for him and what type of spin that he creates on his breaking pitches. Those things start to come together within the last year. He's worked awful hard.”

González lasted three innings and was strong in the first two in his 2020 debut on Monday night against the Giants, but he gave up three runs in the third in the 7-6 Rockies victory. Black said González had trouble loosening in his bullpen session later, and felt more soreness than usual the following day.

“It just didn’t resolve itself, so we decided to take a step back with Chi Chi,” said Black, who added that González stayed in Denver for treatment. “He's getting treatment, feels a little better today, hopefully each and every day he'll feel better and get back on the mound and work his way back to our active roster. In the meantime, we brought up Castellani.”

Hoffman saying in the ‘pen
Righty Jeff Hoffman, who struck out two and forced a key double play in 1 2/3 innings to earn a win in the game González started, had been a competitor for the rotation. But Black views him as part of a bullpen that figures to have a heavy workload during the condensed schedule.

With closer Wade Davis out with a right shoulder strain and Scott Oberg unlikely to pitch this season because of blood clots in his throwing arm, Jairo Díaz has stepped in as closer, and Carlos Estévez and Daniel Bard have filled late roles. Yency Almonte and Tyler Kinley have earned greater opportunity by pitching well.

“There’s going to come a time when we’re going to need all of them -- Jeff Hoffman, Joe Harvey, Phillip Diehl, James Pazos,” Black said. “And they’re all going to have to deliver for us to win ballgames. Carlos, Jairo and Kinley have been out there a lot in the early going.”