ARLINGTON -- The Rangers are counting on starting pitching to be their strongest asset this season, but their rotation may have taken a big hit on Sunday afternoon.

Right-hander Corey Kluber, a two-time American League Cy Young Award winner who is trying to come back from an injury-plagued 2019 season, left his start in Sunday's 5-2 loss to the Rockies after one inning due to tightness in his pitching shoulder.

Kluber was examined by team physician, Dr. Keith Meister, in the Rangers' clubhouse, and he will undergo further examination on Monday. Kluber was replaced by left-hander Joe Palumbo after throwing just 18 pitches.

“Any time your starting pitcher comes out after one inning, you are obviously concerned,” Rangers manager Chris Woodward said. “Hopefully he comes in tomorrow feeling better, but we are obviously taking all the precautions in the world.”

Kluber faced three batters. He struck out David Dahl and walked Trevor Story, who was then thrown out trying to steal second. Charlie Blackmon popped out to end the inning.

According to the Rangers, Kluber said he began feeling his shoulder tighten on him in his first few pitches. He was able to finish the inning, but the shoulder felt progressively tighter and the Rangers made the decision to take him out.

Woodward said that Kluber warmed up fine in the bullpen before the game and there was no inkling of anything wrong when Kluber took the mound.

“He just said a little tightness behind the shoulder,” Woodward said. “So we got him out of there as soon as he felt not normal. He is a tough guy and has pitched a lot of innings in the Majors. When he says something is related to his arm, we are concerned.”

Palumbo went two-plus innings and threw 44 pitches, allowing three runs to take the loss. He and Kolby Allard are considered the Rangers' first line of depth against injuries to the rotation, but the Rangers don’t need an immediate replacement for Kluber.

Texas has three off-days in the first 11 games of the season -- Monday, Thursday and next Monday -- and won’t need a fifth starter until Aug. 8, when they host the Angels.

“Obviously, that would be huge a huge loss. I am not going to sugarcoat it,” said outfielder Joey Gallo, who hit the first homer at Globe Life Field on Sunday. “Kluber is a Cy Young winner we are relying on. We have guys we believe in and trust if we lose Kluber, but it would be a big loss.”

Kluber was making his first start for the Rangers since being acquired from the Indians in a blockbuster trade on Dec. 15. He missed most of last season because of a fractured right forearm (plus a strained left oblique he sustained during the rehab process) and was making his first start since May 1, 2019. And before the injury, Kluber made just seven starts and compiled a 5.80 ERA and 1.65 WHIP over 35 2/3 innings before he went down.

Kluber entered this season as the Rangers' No. 3 starter behind Lance Lynn and Mike Minor. The Rangers were clearly hoping he would be more than that if he could stay healthy, and they were growing optimistic that would happen until Sunday.

Kluber has had no physical issues since being acquired from Cleveland. He pitched four times in Summer Camp and threw at least 80 pitches in all four outings, including 87 in his most recent appearance on Monday. He also made three starts in Spring Training without any problems before the league was shut down on March 12.