LONDON -- Cubs right-hander Marcus Stroman left Chicago's 7-5 loss to the St. Louis Cardinals in the fourth inning Sunday with a blister on his right index finger.

"It did kind of flare up there early on. He did not have it coming into the game," Cubs manager David Ross said. "Those types of things, it's only a matter of time."

Stroman entered the game with an NL-best 2.28 ERA and was 7-0 in his past seven starts going into the series finale in London.

Stroman was pulled with one out in the fourth after Paul Goldschmidt put the Cardinals ahead 5-4 on a sharp single that scored Tommy Edman.

"You could just tell the pitches weren't as sharp as they had been, and we had a fully rested bullpen," Ross said.

Stroman allowed six runs, three earned, and eight hits -- an earlier hit was changed to an error -- and had two strikeouts and a walk.

"Knowing him, he'll be ready for his next start, but I have not talked to the trainers yet," Ross said.