Escalona, 27, was a bright spot for the team last season, going 2-1 with a 2.93 ERA in 49 games, striking out 25 of the 115 batters he faced. Lefties hit just .188/.278/.313 against Escalona last season.
"Obviously, Sergio is an effective left-handed pitcher and we're going to have to find someone to replace him," Astros GM Jeff Luhnow told Brian McTaggart of MLB.com. "It's definitely a setback."
Houston has lefties Wesley Wright and Fernando Abad in camp, as well as Zach Duke, who is competing for a starting spot, but could also be moved to the bullpen.
'This probably makes us think about Duke's role if he doesn't win a spot in the rotation," Lunhow told MLB.com. "[Xavier] Cedeno pitched well, even though he was re-assigned [Friday]. He's pitched well and he's shown he's got some future as a lefty out of the bullpen. There are some options and we're not panicking. We'd prefer to have a healthy Sergio on the team, but it's not to be and we're going to move onto plan B."
Duke, 28, was 1-0 with a 3.86 ERA in 12 relief appearances for the Diamondbacks last season and lefties hit .225/.247/.324 against him (while right-handers hit a robust .353/.393/.498 against Duke).
Escalona pitched in only two spring games after swinging a bat earlier this spring.
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