That issue appears to have gone away, but Morrow is expected to require three rehab starts before rejoining the Blue Jays, and that's going to take some time.
"He's going to throw a side [session Friday], but right now, he doesn't have any pain or issues, and I think we gave it enough time to completely heal and rest," general manager Alex Anthopoulos said Thursday morning. "He was adamant that he felt good."
Morrow believes that the injury was related to his use of a cut fastball. The 28-year-old started throwing the pitch during Spring Training and frequently used it during the early stages of the season.
Left-hander J.A. Happ is also getting closer to a return and could start his rehab stint on Saturday or Sunday in the Gulf Coast League. Happ has been out of action since he was struck in the head by a live drive off the bat of Tampa Bay's Desmond Jennings on May 7.
But the head injury isn't what has kept Happ out of action for such an extended period of time. He also suffered a sprained knee on the play, and it has taken a long time to heal. The veteran left-hander kept his arm in shape during the time off, but he didn't field his position during simulated games and only recently began running sprints.
"The reason it's the Gulf Coast is just because it's the first time not having a screen in front of him -- comebacker, things like that, how will he react," Anthopoulos said. "We can control the environment a little bit more there. We'll see how he does, but he's built up to throw three innings -- doesn't mean he will, but he has gone three innings with an L screen in front of him. If he passes that test, he can move up to the Florida State League, and he should be back very soon."
Gregor Chisholm is a reporter for MLB.com. Read his blog, North of the Border, and follow him on Twitter @gregorMLB. This story was not subject to the approval of Major League Baseball or its clubs.