Shafer was optioned to Triple-A Buffalo on Monday, Shi Davidi of Sportsnet.ca reports.
Shafer was sent to the minors to free up a roster spot for David Phelps (elbow), who was activated from the injured list Monday. The right-hander made two appearances during his most recent stint with the Blue Jays, allowing one run across 3.1 innings while posting a 5:3 K:BB.