This is Sowers' second stint with the Indians. He made a spot start April 26 against the New York Yankees, pitching 5 1/3 innings in a no-decision. Sowers went 2-2 with a 2.21 ERA in seven starts for the Bisons.
To make room for Sowers, the club designated outfielder Jason Tyner for assignment.
Tyner appeared in one game since being called up from Buffalo on May 11. The Indians have 10 days to trade, waive or release him.