Pilkington was optioned to Triple-A Columbus on Thursday.
Pilkington secured a spot on the Guardians' Opening Day roster this year, but he didn't make his major-league debut in any of the team's first six games of the regular season. The southpaw made 22 appearances (21 starts) at the Double-A level last year and posted a 3.13 ERA and 0.99 WHIP in 100.2 innings, and he should now get a chance to face Triple-A competition for the first time. The Guardians haven't yet announced a corresponding move, but it's possible Josh Naylor (lower leg) will be able to return from the 10-day injured list.