Shafer was optioned to Triple-A Buffalo on Sunday.
Shafer has struggled of late, giving up six runs with a 6:7 K:BB over his last 7.1 innings, so he'll make his way to Buffalo. The 26-year-old has been mostly solid for the Blue Jays with a 3.19 ERA over 31 innings this season, so he should rejoin the team after rosters expand in September.