The Cubs have Morrow throwing from 135 feet at the team's complex in Mesa, Arizona, and they're holding out hope he could still potentially return to the big league this season. Morrow's right elbow rehab has gone slowly after surgery last November.
"We've been down this road a few times where he feels good and then he has a setback," Cubs general manager Jed Hoyer said. "I don't want to be over-optimistic. I don't want to be pessimistic.
"We just want him to be healthy. I just feel awful for him. Nobody is more disappointed or more frustrated. Hopefully, this time through, it works for him."
Signed to the Cubs on a two-year, $21-million contract ahead of the 2018 season, Morrow hasn't pitched since last July 15 as his throwing arm first flared up. An attempted return in September was unsuccessful, and Morrow was shut down.
The Cubs signed Kimbrel to a three-year, $43-million deal in early June to address the void at closer without Morrow. Kimbrel threw eight pitches during a brief rehab appearance with the Triple-A Iowa Cubs on Tuesday. He could pitch again Thursday, Hoyer said.
Meanwhile, there's no timetable for a potential return of Morrow to the Cubs.
"Getting him back would be such an incredible bonus for us at this point," Hoyer said. "He could be a real shot in the arm for the bullpen. Kimbrel is coming and our other guys will slot in really well."