Kay was optioned to Triple-A Buffalo on Saturday, Mike Wilner of the Toronto Star reports.
The 26-year-old gave up two runs on four hits and four walks over four innings Friday and has a 6.62 ERA through five outings, and he'll now continue his season in the minors. It's unclear how long Kay is expected to spend at Triple-A, and it's also unknown who will take his spot in the starting rotation.