"We're not going to know about this for a little while, but he feels like it was successful. He had some pain going down his leg, and he said that's gone. So that's a good start."
Morris went on the disabled list last Thursday, and his return this season is questionable, although prior to surgery Morris said he hoped to return to the team in September.
"Obviously it's really early right now," Mattingly said. "He's going to have to recover first and begin all the rehab work."
In 24 games this season, Morris posted a 3.06 ERA with 13 strikeouts and 10 walks over 17 2/3 inning.
Morris said he'd been dealing with the back issue off and on since the 2014 season, the same year he was traded by the Pirates to the Marlins.
Glenn Sattell is a contributor to MLB.com and covered the Marlins on Thursday. This story was not subject to the approval of Major League Baseball or its clubs.