Strop will have an MRI when the team returns to Chicago for the upcoming series against the Reds at Wrigley Field.
"Right now it's sore," Strop told reporters after the game. "It's obviously going to take two weeks, at least, for me to get back on the mound."
Strop didn't overexert himself running down the line until he realized that there hadn't been a throw to first base.
"I was on a good pace, but not like all-out," he said. "But then that last, trying to reach the bag, that was the one that got me."
Maddon had planned to use Strop (6-1) in the bottom of the inning if the Cubs took the lead, even though he had already pitched 1 2/3 scoreless frames to earn the win. Instead, Maddon went with left-hander Randy Rosario, who recorded his first career save.
"You saw how comfortable he was at the plate," Maddon said. "I just didn't anticipate -- I didn't see that coming."
Strop assumed the closer's role after Brandon Morrow was placed on the disabled list for a right biceps injury on July 18. He has converted 11 of 13 opportunities since.
Morrow will likely throw a simulated game over the weekend, and he could return to the Cubs' bullpen as early as next week, though Maddon may not immediately slot him in at the back end.
"Hopefully, it's something simple," said Cubs infielder Javier Baez, who drove in the winning run in the 10th inning on a bunt single. "Because we need [Strop] back. And obviously, we need [Morrow] back, too. With both of our closers now down, [and] it getting close to October, hopefully they get better soon and join the team as soon as they can."