Cueto left Wednesday's 7-2 win over the Cubs after just 3 2/3 shutout innings because of the injury. He was next scheduled to start Monday against Houston.
With the Reds out of the playoff picture, the club could decide to keep their emerging ace out for the rest of the season.
Cueto missed the first five weeks of the year with biceps and triceps issues. He owns a record of 9-5 with a 2.31 earned run average in 24 starts this season.