ARLINGTON -- The Rangers are bracing for the possibility right-handed pitcher Corey Kluber could miss the rest of the season after being diagnosed with a Grade 2 tear of the teres major muscle in the back of his right shoulder.

Surgery is not planned, but Kluber will receive a platelet-rich plasma injection and he'll be shut down from throwing for a minimum of four weeks. That would take Kluber to the end of August and make it difficult for him to build back up as a starter by the end of the season.

General manager Jon Daniels said time is not on the Rangers' side.

“It’s a blow, there is no getting around it,” Daniels said. “Felt like he was in a really good spot, had no physical issues at all. In talking to him today, he feels better than he has in years physically. No indication that this was coming. He was throwing the ball really well. We felt really good about him in the rotation.”

The Rangers are expected to make a roster move in the next couple of days. Left-hander Kolby Allard, already on the active roster, is expected to replace Kluber in the rotation. The Rangers acquired Allard from the Braves on July 30 last season, and he made nine starts for Texas, going 4-2 with a 4.96 ERA and a 1.57 WHIP.

“In most other circumstances, I think we would have penciled Kolby Allard into our rotation and been good with that,” Daniels said. “Would it surprise me if he rattles off 2 1/2 months of really good work? Not at all. It's not fair to ask anybody to be Corey Kluber, but … we have all been impressed, including our veteran pitchers, with Kolby's work."

Kluber, 34, is a two-time Cy Young Award winner with the Indians who was acquired on Dec. 15 in exchange for pitcher Emmanuel Clase and outfielder Delino DeShields.

Texas holds an $18 million option on Kluber for next season. Daniels said it’s too early to assess how the injury will affect the Rangers' decision on picking up that option.

“We acquired him with the mindset he could be here beyond this year,” Daniels said. “This is obviously a physical setback but doesn’t necessarily change our desire to have him back for next year. We need more information before we start talking about that.”

This is the second straight year Kluber has had his season cut short by injury. Last season Kluber made just seven starts for the Indians before being hit by a line drive and suffering a fractured right forearm. He finished with a 5.80 ERA and 1.65 WHIP over 35 2/3 innings.

He entered this season as Texas' 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 had no physical issues up to that point since the trade went down. He pitched four times in Summer Camp and threw at least 80 pitches in all four starts, including 87 in his final outing. He also made three starts in Spring Training without any problems.

“We will give him his period of rest,” Daniels said. “If the injury has progressed to the point where he can begin throwing, he’ll do so with the potential to be possibly ready for the end of the season. If that is the case, it would be more likely as a reliever given the time needed to build up as a starter.”

Left-hander Joe Palumbo replaced Kluber on Sunday. He set down the first six batters he faced before allowing three runs in his third inning. He was also a candidate for the rotation, but the Rangers are going with Allard.

“We talked about it both ways last night,” Daniels said. “We really felt good about it both ways, but probably felt a little bit like Joe was a better option short-term in the bullpen. Obviously that [last] inning, he wasn't quite the same, but that two-inning stint we saw yesterday, we saw that a few times in the training camp. His secondary and his breaking balls, he's got a chance to be a real weapon out of the bullpen, and that was part of the rationale.”