It was yet another setback in the Orioles' quest towards finding a starting shortstop. Castro had started six of Baltimore's past eight games, including the first two against Texas.
"It's feeling better," said Castro, who went 4-for-7 with two runs and two RBIs against the Rangers this weekend, about his groin. "My last at-bat, when I was running to first -- after I ran, I didn't feel anything. But then I started feeling a little tightness in my groin."
Castro was not in the starting lineup on Sunday afternoon, but manager Dave Trembley insisted that the day off had been planned.
"Castro was not going to play today," Trembley said. "This was a day he was not going to play. He's 36 years old, and most times, day games after night games, he probably won't be in the lineup. I think he could play if we needed him, but he's not in the starting lineup today. I'm sure he'll be OK to play tomorrow."
In his stead, Cintron got the start at short. He had hoped to take the reins of the starting role toward the end of June, but he went on the disabled list on July 1 with a left hamstring strain -- an injury that contributed to the Orioles' decision to acquire Castro 18 days later.
Cintron was activated from the disabled list on Aug. 1, but he has started just three games since.
Amanda Comak is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.