Despaigne struggled in a relief outing Thursday, needing 38 pitches to complete an inning and allowing two runs on one hit and four walks. Despaigne was optioned to New Orleans to clear a spot on the active roster for Worley, who signed a Minor League deal with the Marlins in April.
"Probably say the Despaigne outing," said Mattingly, when asked what changed the Marlins' plans for Sunday. "It just didn't go very well and he wasn't as aggressive as we would have liked to see. Obviously, taking almost 40 pitches to get through that inning."
The Marlins have discussed moving Phelps from the bullpen to the rotation, but all parties involved want it to be a permanent move if it indeed happens in the future.
"Phelps, we've said all year long that we're not going to put him the rotation unless we're going to leave him there, and we're just not at that point yet where there's going to be a spot for him, or that we want to make a spot," Mattingly said.
The Marlins are getting left-hander Jeff Locke built up to be a starter. He's currently on a Minor League rehab assignment as he recovers from left shoulder tendinitis. Locke, who began the season on the DL, worked 5 1/3 innings in a rehab outing Friday with Double-A Jacksonville and likely will make one or two more starts in the Minors.
"We've got Locke getting ready," Mattingly said. "He's getting built up to the point where he's getting closer. We're kind of building Jeff to the point of being a starter."
Worley was 2-5 with a 4.43 ERA in 44 2/3 innings in eight starts for New Orleans.
"It could be a little better," Worley said. "I had a few walks down there. But overall, going deep into games like I want, pitching to contact and letting my defense work."
Worley is looking forward to being back on a Major League mound. He last pitched in the big leagues Sept. 22 with the Orioles.
"It's just about executing pitches and getting back out in front of a larger crowd and just competing," he said.
Worley isn't ready to shed his "Vanimal" nickname, either.
"I don't mind it," he said. "I still have people call me that."
• Mattingly spoke glowingly of Hall of Famer Tommy Lasorda, who is resting comfortably in a local hospital with an undisclosed condition. Lasorda, 89, has been with the Dodgers for 68 seasons, and managed the club to two World Series victories. Lasorda is expected to be released from the hospital by the middle of next week.
"He's been a huge figure in the game," said Mattingly, who managed the Dodgers from 2011-15 before being hired by the Marlins. "I think his enthusiasm for the game and how much he loved bleeding Dodger blue is historic. Tommy, I love Tommy. The way he treated me here, he always stayed with me and calling me and things like that. I talked to him just the other day. He sounded OK. I was encouraged hopefully that he's going to recover and get back to being Tommy."