The Guardians optioned Pilkington to Triple-A Columbus on Thursday, Ryan Lewis of the Akron Beacon Journal reports.
Aaron Civale (thigh) completed his second minor-league rehab start Wednesday and looks like he'll be ready to return from the 15-day injured list next week when a fifth starter is needed, so Pilkington was on track to lose his spot in the rotation before being demoted. Pilkington made four starts during his latest stint with the Guardians, submitting a 1-0 record, 4.42 ERA and 1.80 WHIP and 17:11 K:BB in 18.1 innings. He could rejoin the big club before the end of the month, as the Guardians will have a need for a temporary sixth starter due to a June 28 doubleheader with the Twins.