The 29-year-old Hill, who is coming back from elbow surgery, will start Thursday against the Rangers. Left-hander Marc Rzepczynski, originally scheduled to pitch Thursday, will instead pitch Wednesday on three days' rest after having a short outing against the Yankees on Saturday.
Hill, who is from Mississauga, Ontario, is coming back from his second Tommy John surgery and has pitched in the Majors with the Expos, Nationals and Padres. He is 6-2 with a 1.61 ERA in 11 Minor League starts this season, most recently with Las Vegas, where he was 2-2 with a 3.00 ERA in five starts.
Ray, 26, is 6-6 with a 5.51 ERA in 18 starts with Las Vegas. Ray was 1-2 with a 4.44 ERA in four starts with Toronto last year.
The Blue Jays had considered going to a six-man rotation in September to help preserve the young arms in the rotation. But right-hander Brandon Morrow was shut down after his start on Friday because of a buildup of innings.
Toronto no longer considers it necessary to expand the rotation to six, other than a couple of spot starts, because there are two more days off in the schedule. The Blue Jays also had an off-day Thursday.
"We have three days off this month, so we should be fine," Gaston said.