Pedro Strop was hoping to avoid the disabled list, but the Cubs are going to be cautious.
They placed the 28-year-old reliever on the 15-day disabled list Wednesday and he is expected to be sidelined 3-4 weeks with a groin injury.
The first word on the injury became public Tuesday night as Strop allowed three runs to the White Sox and exited the game after a visit with the trainer.
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He said later he had been dealing with the groin issue for five days, though that was news to manager Rick Renteria.
"I didn't think it was an issue, quite frankly," Renteria said before Wednesday's game. "We had kept him out and he kept working. All indications were he was fine."
The rough outing bumped Strop's ERA to 4.97 on the season, with eight walks and 11 hits surrendered in 12.2 innings. He sported a 2.83 ERA and 0.94 WHIP in 37 games with the Cubs last season.
The Cubs called Zac Rosscup back to the big leagues to take Strop's place on the roster. The 25-year-old lefty has appeared in two games in the big leagues and has not allowed a hit or a run.
Rosscup was 2-0 with a 3.00 ERA in nine innings with Triple-A Iowa prior to his promotion.