WEST PALM BEACH, Fla. -- The Astros will be without veteran starting pitcher Lance McCullers Jr. when the season starts in a month after he suffered a small muscle strain his right elbow, which will ultimately put him on the injured list when Houston opens its defense of its World Series title.

The injury is the latest in a series of health setbacks for McCullers, who missed the 2019 season after undergoing Tommy John surgery and the first four months of last season with a right flexor pronator strain. McCullers said his arm became sore shortly after he threw 25 pitches in the bullpen on the back fields at Ballpark of the Palm Beaches on Feb. 14. An MRI performed Tuesday showed no structural damage, but McCullers won’t be able to throw for a couple of weeks.

“I had a great offseason and was excited for the year,” McCullers said. “I felt like I was in an amazing spot physically and got to camp early. I threw a bullpen here last Tuesday and unfortunately, after that bullpen -- nothing during the bullpen raised any red flags -- but after the bullpen and into the evening and into the next day, I had some elbow soreness.

“I’ve been a little bit upset. I was really looking forward to a great start to the camp and great start to the season. Any time this happens, it’s very frustrating for me and the team and the fanbase. I just wanted to have a great year and get off to a great start and unfortunately that didn’t happen.”

Having already lost pitcher Justin Verlander -- the 2022 AL Cy Young winner -- to the Mets in free agency, the Astros will now have to lean into their starting pitching depth. The rotation without McCullers is headlined by All-Star left-hander Framber Valdez, followed by Cristian Javier, José Urquidy and Luis Garcia. Rookie right-hander Hunter Brown likely makes the Opening Day rotation.

McCullers went 4-2 with a 2.27 ERA in eight starts in August and September of last year and made three starts in the postseason, including a Game 3 World Series start in which he gave up five homers at Philadelphia. McCullers signed a five-year, $85 million contract extension in March 2021 and responded with his best season, going 13-5 with a 3.16 ERA in 28 starts.

McCullers, 29, now faces another long rehab for the second year in a row, but hopes to be able to contribute more than he did last year.

“The smartest thing would be [to] go at a small pace and come back and still be ready to throw a majority of a full season,” he said. “I still hope to hit that 150, 160 innings mark, versus rushing it and coming back and risking re-injury or risking not being able to be an effective part of the team.”

McCullers said he started playing catch earlier in the offseason. He picked up a baseball in mid-November and played catch the entire offseason without any issues. Even while throwing numerous times in the bullpen at Minute Maid Park in the winter, he had no problems.

“I don’t know if it was too much too soon,” he said. “I didn’t feel like that. I felt like I had a good, healthy offseason and that was kind of a normal progress.”

Still, McCullers said the MRI results were a relief in that there is no structural damage. He said team doctors have been in consultation with Dr. Neal ElAttrache, who performed his Tommy John surgery, and McCullers plans to speak with him about the diagnosis.

“It’s been a tough couple of days just having to come to the reality that I’m not going to be a part of the team to open the season and I’m going to have to undergo another rehab,” he said. “When the one thing that you’re great at and you’re not able to do because the vessel you do it through -- my body -- sometimes won’t let me, I think that’s very tough to process and sometimes can feel like you’re on a little bit of a hamster wheel at times. Overall, everything is good and the MRI makes me feel very confident.”