Aoki, 35, went to the Blue Jays in the trade that sent Francisco Liriano to the Houston Astros. In 12 games for the Blue Jays, he hit .281 with 3 home runs and 8 RBIs.
"It wasn't easy," Toronto manager John Gibbons said of the decision on Aoki, according to MLB.com. "The guy's played great for us. We need to keep some extra arms. The way things have been going, we need to keep that extra bullpen arm and then in a few days we expand anyway."
Major league rosters will expand starting Friday, allowing the Blue Jays to take a look at some young outfielders, including Teoscar Hernandez, a highly-rated prospect who came to Toronto with Aoki in the Liriano trade.
The Blue Jays recalled reliever Leonel Campos from Triple-A Buffalo to fill Aoki's roster spot.