Phillies right-hander Jesen Therrien underwent Tommy John surgery earlier this week and could miss the entire 2018 campaign as a result, as Jeremy Filosa of 98.5 FM Sports in Montreal (Therrien’s hometown) first reported, on Twitter.

The 24-year-old Therrien made his Major League debut this season, appearing in in 15 games and totaling 18 1/3 innings. As Matt Gelb of the Philadelphia Inquirer notes, his 92.6 mph average fastball in the bigs was diminished from his minor league velocity, and Therrien’s results were nowhere near the promising output he showed in the minors. Therrien obliterated minor league opponents, posting a ridiculous 1.41 ERA with 10.2 K/9 against 1.4 BB/9 in 57 1/3 innings between Double-A and Triple-A. In the Majors, he logged an 8.35 ERA on 24 hits and seven walks with just 10 strikeouts.