Scheppers said Sunday the knee has been bothering him for about a week, but he initially thought it was regular soreness. Rangers manager Jeff Banister said he became aware of the issue in the New York series, but Scheppers wanted to pitch through it.
Matters changed after Scheppers' rough appearance Sunday. Banister has defended Scheppers, saying two of the three hits he allowed were bad luck, but he also acknowledged Scheppers certainly was not at his best.
"You look at performance, but within the performance you have to look at the execution of the pitch, I think just how sharp everything is," Banister said. "He looked to be a tick down in the [velocity] last night when you go back and look at it. That's part of the whole process."
Scheppers is 4-1 this season with a 5.66 ERA in 38 appearances. He also opened the year on the disabled list with a right ankle sprain.
Klein makes his fourth stint with the Rangers this season. He is 1-0 with a 5.82 ERA in 10 Major League games this year. He is 1-0 with a 0.91 ERA in 12 games in Triple-A.
The move continues the Rangers' attempt to fortify a bullpen that entered Sunday with the league's highest ERA at 4.73. Scheppers was typically the Rangers' eighth-inning option, and Banister said for now, there is no clear setup man.
"We'll continue to look at the matchups for us," Banister said. "We'll get to know [Sam] Dyson a little better, see where [Jake] Diekman and [Sam] Freeman fit into that, along with [Spencer] Patton."
• Klein will wear No. 43 for the Rangers. His usual number, 35, now belongs to Cole Hamels, whom the Rangers traded for Friday.
• The Rangers' 29 pitchers used this season is tied with the Yankees for most in the American League and trails the Braves at 31 for most in the Majors.
• Catcher Bobby Wilson had two hits and two RBIs Saturday in his Rangers debut, but Chris Gimenez was in the Rangers' starting lineup at catcher Sunday. The Rangers have already used four different catchers since the All-Star break.
Cody Stavenhagen is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.