HOUSTON -- The Astros are preparing for life without Lance McCullers Jr. in the American League Championship Series -- and perhaps beyond -- while they await the results of an MRI performed on their ace pitcher, who left Game 4 of the AL Division Series after four innings with tightness in his right forearm.

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McCullers, who wasn’t available to the media during Thursday’s workout at Minute Maid Park, underwent an MRI late Wednesday or early Thursday, according to Astros general manager James Click. He said the initial diagnosis is forearm tightness and that the team was awaiting further test results.

“Obviously, any time you have a pitcher coming out with a forearm anything, you want to take your precautions and just make sure you know exactly what’s going on,” Click said. “He did go for an MRI, just precautionary to make sure everything’s OK in there. We’re waiting for those images to be reviewed and get an examination on them.”

The Astros haven’t officially ruled McCullers out for the ALCS, at least publicly, but they are expected to add some pitchers when the roster for the best-of-seven series against the Red Sox is set by 10 a.m. CT Friday. McCullers signed a five-year, $85 million contract extension in the spring that’s set to begin next year and responded with the best year of his career, going 13-5 with a 3.16 ERA that was second in the AL.

“He’s going to be here for a long time, and we have to balance that against this,” Click said.

Astros manager Dusty Baker said Thursday that left-hander Framber Valdez will start Game 1 on Friday, followed by right-hander Luis Garcia in Game 2 on Saturday.

If McCullers misses the ALCS, it’s probably not realistic for him to be able to return for the World Series, either, if the Astros advance. McCullers pitched in relief through a torn ulnar collateral ligament in his right elbow during the 2018 ALCS against the Red Sox and eventually underwent Tommy John surgery. He missed the entire 2019 season.

“There was a low level of concern when he initially came out of the game, so that’s kind of the state we’re in right now,” Click said. “It was just precautionary. Sometimes when you’ve got a little bit of forearm tightness, if this were the regular season, you just shut him down for two weeks and you wouldn’t think anything of it. Obviously, this is the postseason and it’s a different animal.”

McCullers would not have been available until Game 3 had he been healthy. Right-hander José Urquidy, who would have started Game 3 of the ALDS on Monday had it not been pushed back a day because of rain, is Houston’s likely Game 3 starter if McCullers is out. Urquidy would be pitching for the first time in 15 days.

But who would start for the Astros in Game 4?

Zack Greinke and Cristian Javier, a pair of starters who were in the bullpen in the ALDS, would be in the mix along with Jake Odorizzi, who was left off the ALDS roster. Or the Astros could use a combination of two of them.

Greinke threw one inning in Game 3 of the ALDS and hasn’t started since Sept. 19 (68 pitches). Javier appeared in 27 games in relief after starting the season in the rotation and threw 56 pitches -- his most in four months -- in 2 2/3 innings in relief in Game 3 of the ALDS. Odorizzi went 1-1 with a 2.93 ERA in his final seven starts to end the season before being left off the ALDS roster. He hasn’t pitched since Oct. 2.

“We're still talking about things, and we do have a few guys that are hurt that we're trying to figure out to take the best roster forward,” Baker said.

The Astros carried 12 pitchers in the ALDS and will likely add at least one more to their roster in a series that could include games on three consecutive days in Games 3-5.

“I would imagine that’s going to be a heavy consideration, but we’ve also got to make sure we’re not overdoing it and sacrificing anything on the position-player side by making sure we have coverage on the pitching side,” Click said.