Romero suffered the injury during his last start against the Yankees when he fielded a line drive off the bat of Mark Teixeira.
"There has been some improvement since the game that night," Blue Jays manager John Farrell said following his club's 3-2 victory over Tampa Bay on Wednesday night. "He threw on the mound today just to test it out before tomorrow. He was able to throw but yet, at the same time, he felt like it was tolerable.
"The fact that it's tolerable, I think, is enough information that we need to bump him back a couple of days."
Romero will be pushed back two days and is tenatively scheduled to start on Saturday afternoon against the Tigers. Right-handers Kyle Drabek and Jesse Litsch will each move up one day and start on Thursday and Friday, respectively.
Farrell said there are no restrictions with Romero's arm but the club wanted to take a cautious approach and delay the next scheduled outing.
"We don't want to take any chances and it's as much precautionary as it is anything else," Farrell said. "It's one of those injuries if you risk it, you could be looking at prolonged down time."
Romero is 2-3 with a 3.00 ERA in six outings this season. The 26-year-old has struck out 41 while walking 13 over 39 innings.