It's the second setback in several weeks for Morrow, who went 13 days between starts in May due to soreness in his upper back and neck area.
"It just hasn't recovered enough to go out there and make the start," said Morrow, who is 2-3 with a 5.22 ERA this season. "It's really just a matter of being able to be competitive with it. I mean, there are things that I can throw through but this, you know, not really any point if you don't think you can be competitive.
"The plans are right now not to leave the team and then be able to throw right when I come off the [DL]."
The stint on the disabled list begins just three days before the Blue Jays are set to welcome back right-hander Josh Johnson from the 15-day DL. Johnson's return was expected to help stabilize the rotation, but the group has once again been thrown into a state of flux due to injury woes.
Veteran right-hander Ramon Ortiz was promoted from Triple-A Buffalo to make Morrow's scheduled start on Sunday in San Diego. Ortiz was designated for assignment by the Blue Jays on May 29 and was then outrighted to Buffalo.
Ortiz normally would have had to wait 10 days before rejoining the Blue Jays, but that time period was waived due to Morrow's injury. Players can be brought back to the big leagues quicker than 10 days if someone is placed on the disabled list.
The 40-year-old Ortiz has made three starts for the Blue Jays this season and has an ERA of 5.01 in six appearances. He didn't pitch for Buffalo during his absence, but should still be appropriately stretched out to give Toronto some much-needed innings.
The injury isn't expected to keep Morrow out for very long, but that has done little to ease his level of frustration.
"I haven't been healthy a whole lot this year, so it's kind of been tough on that aspect of it, but hopefully I'll just fully recover from this and be feeling good in the next couple of weeks," Morrow said.
"There was no structural damage and [the MRI] didn't really show inflammation or anything like that, so that's good. But you don't treat the MRI, you treat your symptoms and stuff, and it's still sore. Playing catch, I just wasn't able to really put anything on it and it's still feeling the same."
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.