Astros interim manager Tony DeFrancesco said Fernando Abad, who strained his right oblique in Monday's game, probably won't make his next start.
Edgar Gonzalez strained his hamstring in Friday's game and threw a bullpen session on Tuesday. DeFrancesco said Gonzalez's availability for his next start -- scheduled to come on Friday in Milwaukee -- is up in the air.
Lucas Harrell, who has pitched a career-high 182 2/3 innings entering Tuesday's start, may not get another outing. Bud Norris, managing a blister problem and a skin irritation on his scalp, will start on Wednesday, but his availability for the final series in Chicago could be a question mark.
That leaves Jordan Lyles and Dallas Keuchel as the only totally healthy starters in the Astros' six-man rotation. The club will probably revert to a five-man rotation until the end of the season.
"We're kind of banged up right now, but we're just trying to piece together our starting rotation for the next five days," DeFrancesco said.
Fernando Rodriguez is the most likely candidate for a spot start. Rodriguez threw a career-high 72 pitches in 4 1/3 innings of emergency relief on Monday.
"He won't be available for a few days, but in five days, he could be one of the starters in Chicago," DeFrancesco said. "It's going to be day to day with the rotation. It's unfortunate, but September baseball just seems to get harder and harder right now."
The injuries aren't limited to the rotation. Third baseman Matt Dominguez has flu-like symptoms and wasn't at the ballpark on Tuesday. Infielder Marwin Gonzalez is day to day with a sprained left ankle.