MINNEAPOLIS -- Brusdar Graterol was discouraged. Again.

Three years after Graterol was shut down for more than a full season by Tommy John surgery, he found himself on the sidelines once more. This time, the issue was a right shoulder impingement that shut down the Twins' top pitching prospect, per MLB Pipeline, in May following a dominant 6-0 start with a 1.71 ERA at Double-A Pensacola.

"I thought I wasn’t going to get to where I did get with my injury," Graterol said recently at the MLB/MLBPA Rookie Career Development Program in Miami. "I told myself that I was going to work harder than I was working, and that I wanted to get to the big leagues."

As Twins fans now know, that work paid off when the club gave Graterol a taste of the Major Leagues last September, and the right-hander eventually pitched his way onto Minnesota's roster for the American League Division Series against the Yankees.

At the time, the callup was a move borne in curiosity and an upside for the club as much as anything else; when the fireballer arrived in the Twins' clubhouse at Comerica Park for the first time, pitching coach Wes Johnson and assistant pitching coach Jeremy Hefner didn't know what they would see from the kid.

Fast-forward a few months, and there's still some uncertainty in Graterol's situation. But this time, it's not a question of if he will impact the Major League club at some point this season, but one of how -- will the right-hander transition back to a starting role, or will he remain in the bullpen to see how much his fastball in the triple digits can play up in the late innings?

For now, the Twins' rotation is an area of greater need than the bullpen, but Graterol could first require an acclimation back to starting with Triple-A Rochester. Either way, the arm talent should flourish at some point for the Twins' most heralded pitching prospect since José Berríos, and accordingly, Graterol said that his offseason focus has been more on the mental side of the game.

"My preparation for 2020 is to be more ready mentally, keep working and keep myself healthier, with a positive mind and doing the job that we have to do," Graterol said.

Graterol already feels much better off in that sense after his big league cameo, which initially saw the right-hander allow three runs without recording an out in his first high-pressure situation (and third Major League game) on Sept. 6 against Cleveland before he finished the season with a 1-2-3 inning in ALDS Game 1 at Yankee Stadium, featuring a battle against Edwin Encarnación that Graterol still remembers with a great deal of pride.

"He’s a hitter with a lot of power and intelligence," Graterol said. "I feel that I faced him with all the guts I have. I tried to win the battle and I did, in fact. I felt proud to face a hitter like him, with so much experience. I think that just in that one moment I learned a lot of things. But I’d like to face a lot of players with power, strength, intelligence. I think that’s going to help me, all of that."

That progress didn't go unnoticed by manager Rocco Baldelli, who spoke highly of Graterol at the Winter Meetings in December but reiterated the organization's desire to be cautious with Graterol and keep his health and long-term development in mind. The 21-year-old has eclipsed 61 innings in only one professional season: in 2018, when he threw a career-high 102 frames.

But for now, there's no need for Graterol to be discouraged anymore. He should be at the head of the arrival of a major wave of top pitching prospects in 2020, which could also feature Jordan Balazovic (No. 4) and Jhoan Duran (No. 9) -- and unlike the others, he's already shown that he can handle the pressure of the game's highest level.

"He was able to focus very well toward the end of the year and deal with some fairly difficult situations," Baldelli said. "Emotional games, meaningful games in September and October. None of that noise really bothered him at all. Literally, you could go and talk to him and he was just a cool cat and very relaxed in the dugout, and whatever you asked him to do, he would do it, basically is the mentality he has. That's impressive."