ST. LOUIS -- The Pirates were expected to call up Roansy Contreras at some point this season. It was a matter of when, not if. Due to circumstance, Contreras is back sooner than planned.

Contreras, the Pirates’ No. 5 prospect per MLB Pipeline, was called up Saturday morning to replace Duane Underwood Jr., who left Thursday's Opening Day game with a right hamstring strain.

The move to bring up Contreras, who was scheduled to start on Saturday for Triple-A Indianapolis, was made out of necessity. With Underwood headed to the injured list, Contreras was the only healthy pitcher on the 40-man roster who wasn’t already with the Major League team.

Right-handers Blake Cederlind (right elbow) and Nick Mears (right elbow) are on the 60-day injured list. Left-hander Sam Howard (back muscle strain) and righties Max Kranick (right forearm strain) and Luis Oviedo (right ankle sprain) are on the 10-day injured list. Right-hander Adonis Medina was designated for assignment when the Pirates signed catcher Andrew Knapp and outfielder Jake Marisnick. The Pirates’ only other option, whether internal or external, would have involved designating someone else for assignment.

There are two central questions to address with Contreras, who made his Major League debut last September in Pittsburgh. First, there's the matter of his role. The Pirates etched out their plans for the first time through their rotation -- Mitch Keller, Bryse Wilson, Zach Thompson and José Quintana will pitch the next four games, in that order -- but the plan after that is ambiguous. Manager Derek Shelton has said repeatedly that the rotation will be “fluid." Now, maybe that fluidity involves letting Contreras get some starts.

The second question pertains to the length of his stay. Given that the plan was for Contreras to begin the season with Indianapolis, it’s possible that Contreras will spend time with the Pirates until another pitcher on the 40-man roster gets healthy. Those plans could very well change if Contreras pitches well, but only time will tell.

The circumstances for Contreras’ arrival aren't ideal given that it took several pitchers getting injured, but with the opportunity, the 22-year-old will have the chance to absorb more experience -- and potentially earn staying power.

Contreras is coming off a phenomenal season with Double-A Altoona. Across 12 starts, he logged a 2.65 ERA, striking out 12.6 batters per nine innings while only walking two batters per nine innings. Contreras made a spot start with Indianapolis, then earned him a cup of coffee with the Pirates at the tail end of last season, where he threw three scoreless innings with four strikeouts in his Major League debut.

“[The debut] helped me a lot,” Contreras said through team interpreter Mike Gonzalez during Spring Training. “I was able to identify that it's the same game. Just going out there, dominate, being able to control the game, control my mindset, control my physical body and be able to dominate. … The game is quick, but it’s still the same game.”