Stein said there is no specific date for Morrow's surgery, but it will most likely be within the next week.
Morrow, who hasn't pitched in a game since May 2, had two setbacks during separate Minor League rehabilitation stints. The first occurred on June 7 during a start for Double-A San Antonio and the second on July 25 for Triple-A El Paso. Each time, Morrow experienced discomfort in his shoulder.
"He has kind of built back up through rehabilitation a couple times, he's gotten to the point where he was able to cut it loose, go into one game and then recovery isn't quite there," Stein said.
In November Morrow signed a one-year deal for $2.5 million with the possibility of earning $5 million in incentives. The right-hander was 2-0 with a 2.73 ERA in five starts before going on the disabled list in late May with right-shoulder inflammation.
Stein said that the recovery time for Morrow is three to four months.
"I would like to be able to come back and pitch, obviously, but it's nice to think that you wouldn't have any recurring incidents of it and going forward you won't have any more soreness or the same thing happening again," Morrow said Friday. "I think in the long run it will be good. Obviously disappointing and frustrating right now."
Beth Maiman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.