PORT ST. LUCIE, Fla. -- Considering veteran first baseman Christian Walker has dealt with some oblique injuries in the past, the Astros decided to send him back to Houston on Thursday night to undergo an MRI to determine the extent of the left oblique injury he suffered Wednesday.

"This is an injury that happened to him in the past and he walked in feeling pretty good about things, but we want to make sure,” Astros manager Joe Espada said.

Walker, who was scratched from the lineup Wednesday after feeling some pain during batting practice, said Thursday he was still a little sore, but improving.

"These next few days will tell us a little bit more with how it responds, but so far I’m hopeful, for sure,” he said.

Walker missed more than a month last season while he was with the D-backs due to a strained left oblique. He said this injury doesn’t feel as serious as that one, but more will be known after he undergoes imagining.

"It’s going to get worse swelling-wise before it starts to feel better,” Walker said. “You kind of got to let your body go through the process. So far today, it feels pretty good.”

Walker was taking batting practice in a batting cage Wednesday morning in West Palm Beach when he felt some tightness in his left side. He told Espada at that point he was going inside to be examined by the team’s athletic trainers.

"I'm a little familiar with oblique stuff, but once I felt that just tried to not push it given the time of the year and the timeframe and all that,” Waker said.

The Astros signed Walker to a three-year, $60 million contract in December as their biggest offseason addition. He’s appeared in four Grapefruit League games this spring, going 4-for-8 with three doubles and two walks. Jon Singleton, who made the most starts for the Astros last year at first base, started his fourth consecutive game at first base on Thursday against the Mets at Clover Park.

Zach Dezenzo, ranked as the team’s No. 5 prospect by MLB Pipeline, can also play first base, along with backup catcher Victor Caratini.

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Despite missing a month last year with the oblique injury, Walker finished with 26 homers and 84 RBIs in 130 games for the D-backs. The 33-year-old has quietly established himself as one of the game’s top first basemen over the past three seasons, pairing strong production at the plate with elite glove work. He’s won three consecutive National League Gold Glove Awards at first base.

The right-handed slugger ranks fifth among primary first basemen with 11.4 WAR (per Baseball-Reference) since the beginning of 2022, recording 95 homers, 281 RBIs and an .813 OPS (123 OPS+) over 1,880 plate appearances and leading the position with 38 outs above average in that span.

The Astros signed him after trading Kyle Tucker to the Cubs and before Alex Bregman signed with the Red Sox and he’s expected to hit in the top four spots in Houston’s lineup.

Singleton, who spent the entire 2024 season on a Major League roster for the first time in his career, lost 25 pounds in the offseason to get lighter on his feet. He hit .234 with 13 homers, 13 doubles, 42 RBIs, 47 walks and a .707 OPS in a career-high 119 games in ‘24 and would be the starter if Walker begins the year on the injured list.