HOUSTON -- The Astros will be without one of their key relief pitchers for the American League Division Series. Right-hander Kendall Graveman, whom the club acquired from the White Sox in a trade in July, was left off the roster for the series against the Twins while he deals with right shoulder discomfort.

Graveman, who appeared in 23 games with the Astros this year and posted a 2.42 ERA, believes the issue began while pitching in Boston in late August, and he hopes the rest in the Division Series will allow him to be able to be activated if the Astros advance. Graveman could be added to the ALCS roster.

“Kind of been going on for a little bit and been pitching through it, and I got to the point I needed some time, so the goal was to try to get ready if we advance any further,” Graveman said. “If we’re fortunate enough to play any further after this series, hopefully I can be ready.”

With Graveman out, the Astros carried 12 pitchers on their ALDS roster, with Graveman and lefty reliever Bennett Sousa as the two players dropped from Houston’s 28-man regular-season roster from September. Astros general manager Dana Brown said Sousa would have made the roster had he been eligible; he was claimed off waivers Sept. 3, which is after the deadline to be playoff eligible.

Graveman said his shoulder was bothering him when he pitched in Arizona in the final series of the regular season and he was hoping the five-day break prior to the start of the ALDS would give him enough time to feel better.

“But that’s not the case and now we have to continue to work,” Graveman said. “It’s never a good time to miss games and miss time on the field, and I hate that. I’ve been fortunate to be healthy for the past three years and perform and pitch. It’s one of those things I need to take a few days, give it time to heal and come back sooner than later.”

The Astros have four players on their ALDS roster with no postseason experience: catcher Yainer Diaz, right-hander J.P. France, infielder Grae Kessinger and first baseman Jon Singleton.