Left-hander Brett Cecil was recalled from Triple-A Las Vegas on Friday to take the spot of injured starter Brandon Morrow. Kyle Drabek and Drew Hutchison have since joined Morrow on the disabled list to create an additional two openings.
Triple-A right-hander Jesse Chavez is an early favorite for one of jobs, while long reliever Carlos Villanueva made a case for himself with four scoreless innings of relief on Friday night.
"[Villanueva is] in the mix, yeah," Blue Jays manager John Farrell said. "Yet, we haven't determined who's going to start on Wednesday. I don't have anything more definitive than that for you right now."
Villanueva served in a similar role last season. He began the year in the bullpen, but eventually transitioned to the rotation following a series of injuries and subpar performances by the starters.
The 28-year-old was effective in that role until he began dealing with a right-arm injury. He went on to post a 5.15 ERA in 13 starts. In the past, Villanueva has expressed a desire to return to the starting rotation and believes he is more suited for that job than he was in 2011.
"I pitched two months with a little bit of pain in my elbow, but it was just fatigue," Villanueva said of last season. "I just hadn't prepared for that the season before. I'm coming from a season that I threw 50 innings, and all of a sudden I'm over the 100-inning mark.
"But this offseason, actually, I prepared all the way around. It's better to prepare to start, throw 180 innings and then take it down from there than have to build up during the season. My arm has been treating me well throughout my career, so I don't expect anything different."