The loss of Morrow for the rest of the season is another blow to a Blue Jays team that is in desperate need of reliable starting pitching, but at least they now know what's wrong with their hard-throwing righty.
"I think there was speculation, because they couldn't see anything on an MRI, that they thought it was a nerve issue," manager John Gibbons said.
"They look at the MRI, they don't see any structural damage, so the doctors figure it might be something with the nerve. They're always trying to come up with an answer."
Morrow will rest for six weeks before eventually beginning a throwing program. The goal is to have him pitch off the mound by the end of the season, so the club can have a better idea of his progress before closing up shop for the year.
The recovery is key, because the Blue Jays will be relying on him for a return to form next year. He is signed through 2014 with a club option for the following season. Morrow has arguably the best stuff of anyone in Toronto's starting rotation, but he has yet to throw more than 180 innings in any of his seven seasons in the Major Leagues.
Morrow's 2012 season was derailed for more than two months because of a torn oblique muscle, and earlier this year, he battled upper back and neck problems. The forearm issue then surfaced, and despite multiple attempts at rehabbing the injury, he will now require a prolonged period of rest.
"You figure at the end of six weeks, he'll be feeling better, but I'm no doctor," Gibbons said of Morrow, who finishes the season with a 2-3 record and 5.63 ERA in 10 starts.
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.