ARLINGTON, Texas (CBSDFW.COM/AP) – The Rangers biggest offseason acquisition, two-time Cy Young Award winner Corey Kluber, will miss at least four weeks after being diagnosed with a grade 2 tear of the teres major muscle in the back of his right shoulder, team spokesperson John Blake said on Twitter Monday.

Kluber’s Texas debut lasted just one inning on Sunday.

He had an MRI Sunday evening.

The right-hander threw just 18 pitches against Colorado on Sunday before departing his first start in almost 15 months with shoulder tightness.

“Given the time frame here and the nature of a 60-game schedule and everything that goes with it, the timeline is not on our side,” Rangers General Manager Jon Daniels said. “We will give him his period to rest, and then if it’s recovered, or the injury is healed to the point where he can begin throwing, he’ll do so with the potential to possibly be ready for the end of the season. If that is the case, it’d probably be more likely as a reliever, given the time needed to build up as a starter.”

The Rangers, who acquired Kluber in an offseason trade with Cleveland, said Kluber reported feeling the tightness in the first few pitches and it got worse as the inning progressed. He was examined by a team doctor and will be further evaluated Monday.

READ MORE: Shootout With Mexican Soldiers, Police Leave 9 Suspects Dead Near US border

The 34-year-old Kluber was knocked out of his last start for the Indians on May 1, 2019, when his right forearm was broken by a comeback liner.

On Sunday, Kluber struck out leadoff hitter David Dahl and walked Trevor Story, who was thrown out trying to steal before Charlie Blackmon popped out. Kluber was replaced by left-hander Joe Palumbo.

Kluber didn’t speak to reporters after the Rockies’ 5-2 win. Manager Chris Woodward said there was no indication of trouble for Kluber after he warmed up. There was no update on Kluber’s condition after the game.

“He is a tough guy and has pitched a lot of innings in the majors,” Woodward said. “When he says something is related to his arm, we are concerned. Hopefully he comes in tomorrow and feels a little better, but we’ll see.”

Kluber’s five-year run as an opening-day starter ended with the former Cleveland ace starting the finale of the Rangers’ opening series in their new $1.2 billion retractable roof stadium.

The early departure was essentially the second time Kluber’s return was short-circuited since breaking his forearm. He was close to coming back last season when he sustained an oblique injury during a rehab start last August.

Going into the 2019 season, Kluber was on a five-season stretch as one of baseball’s best pitchers. He was a 20-game winner in 2018, and the AL Cy Young Award winner in 2014 and 2017. The three-time All-Star threw at least 203 innings with 222 strikeouts or more each season.

Before his Texas debut, Kluber made all 208 appearances and 203 starts with the Indians over nine seasons. He is two wins shy of 100 for his career.

MORE NEWS: Texas Amber Alert Issued For 6-Year-Old Amari Daniel Baylor

(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)