Phillies reliever Jesen Therrien undergoes Tommy John surgery

PHILADELPHIA, PA - OCTOBER 3: A general view of the game between the Miami Marlins and Philadelphia Phillies on October 3, 2015 at Citizens Bank Park in Philadelphia, Pennsylvania. The Marlins defeated the Phillies 7-6. (Photo by Mitchell Leff/Getty Images)
PHILADELPHIA, PA - OCTOBER 3: A general view of the game between the Miami Marlins and Philadelphia Phillies on October 3, 2015 at Citizens Bank Park in Philadelphia, Pennsylvania. The Marlins defeated the Phillies 7-6. (Photo by Mitchell Leff/Getty Images) /
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Phillies reliever Jesen Therrien received Tommy John surgery earlier this week and it appears likely he will miss all of 2018.

The Phillies have lost one of their more exciting relief prospects for potentially all of 2018 as Jesen Therrien underwent Tommy John surgery earlier this week according to Matt Breen of Philly.com. The righty is expected to miss most, if not all of the 2018 season as he recovers from the surgery.

Therrien inserted himself into the conversation this season with a strong minor-league campaign. He opened up the year with Double-A Reading, striking out 39 batters in 28.2 innings while posting a 1.26.

After being promoted to Triple-A Lehigh Valley, Therrien continued to be effective, compiling a 4.33 strikeout-to-walk ratio, 1.57 ERA, and 1.08 WHIP. His strikeout rate dipped compared to Reading, but it was still pretty high at 22.2 percent.

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The team was really high on Therrien, with his slider being compared to Brad Lidge’s back in 2008. Joe Jordan, director of player development, liked what he saw from Therrien earlier in the season in Double-A: [quote via Jim Salisbury of CSN Philly]

"“He’s 93-94 with his sinker and his slider is a finishing pitch,” Jordan said. “He’s got as good a breaking pitch as anyone in our minor-league system.“The slider has two shapes, one that he throws for a strike, one that he uses to finish a hitter. It’s got power at the end and downward finish.“He’s been spot-on all year with a combination of stuff and execution. This is the guy we’ve been waiting for. He’s shown it in the past. He’s just been inconsistent. But he came into camp this spring in good form and has been consistent night in and night out.”"

Manager Pete Mackanin was a fan of Therrien’s after seeing how he pitched in spring training: [quote via Breen]

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"“We loved him in spring. I loved his breaking ball,” Mackanin said. “We really got excited about his breaking ball. He has a really nasty breaking ball. It’s good to see.  …  He’s on the map for me based on what I saw in the spring. He came in, and threw strikes with a really good looking breaking ball. Especially out of the bullpen, if you have a really good breaking ball and you can command it, that’s half the battle.”"

After coming up to the majors, Therrien struggled. As a whole, he had an 8.35 ERA in 15 appearances.

He put together a nice string of outings where he had a 2.45 ERA between Aug. 11 and 22, which included pitching twice in the same day during a doubleheader. However, he started getting shellacked in his last few outings before landing on the disabled list.

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With Therrien likely on the shelf next season, he will miss out on a crucial time in the Phillies bullpen as the team tries to figure out which relievers they want to keep in the majors. All that is on his resume is this one poor stint, so it will be harder for him to stay in the majors long-term.