Mattingly said that it's unlikely that Morris will return in the near future. He declined to suggest or deny that surgery will be needed.
"It doesn't feel like a 15-day thing," Mattingly said. "I think B-Mo -- he can speak for himself because he's kind of mulling his options with what he wants to do, how he wants to attack this thing. It's a little more complicated than just give him a couple days' rest, and he's going to be fine. He has had enough fight with that."
Added Morris: "Surgery is an option, yes. At this point, surgery is the only option that can fix what is the issue."
Morris posted a 3.06 ERA with 13 strikeouts and 10 walks in 24 appearances this season. He last appeared in a loss to the Rays on Tuesday at Marlins Park, where he allowed one run and one hit with one strikeout in a frame.
"I wasn't doing myself any justice, and I wasn't helping the team out right now, because I feel like I'm pitching at 16 percent," Morris said. "So I don't feel like I can get my body in the right positions, and I'm just not capable of doing what I want to do."
Wittgren tossed a scoreless ninth in Thursday's 9-1 win over the Rays. He compiled a 3.18 ERA with five strikeouts and four walks in four appearances spanning 5 2/3 innings with the Marlins earlier this season before being sent down. Miami's 21st-ranked prospect, according to MLBPipeline, was 1-0 with a 1.42 ERA and 11 strikeouts in 10 appearances with the Zephyrs in 2016.
"I'm just going to keep approaching hitters like I have been," Wittgren said before the game. "I've got to get ahead in the count. The first few outings I kind of fell behind a little bit."
• Right fielder Giancarlo Stanton remained out of the lineup on Thursday after missing Wednesday's win over the Rays with right side soreness. Mattingly said he didn't consider placing Stanton in the lineup with the afternoon start time.
"It was a matter more of, 'It's going to be a day game, I'm not going to fight it,'" Mattingly said. "Hopefully, tomorrow we'll see where we're at."
• Left fielder Christian Yelich said he remains day-to-day with back spasms. Mattingly said he's hopeful Yelich will be ready when the Marlins face the Braves on Friday at Turner Field.
"I'm hoping he would be ready tomorrow just because you're back in the National League, and you need your guys," Mattingly said. "But it's also something where I don't want to say tomorrow is the day, and we get there and he tries to force himself into tomorrow."
• Left-hander Tim Berry cleared waivers and was outrighted to Class A Advanced Jupiter.