MIAMI -- The Marlins are making a rotation change, adding Elieser Hernandez and moving Trevor Richards to the bullpen.

Richards (3-12, 4.62) opened the season as the No. 2 starter, but coming out of the All-Star break, he was lined up fifth. The switch also comes at a time when Richards is attracting trade interest.

Hernandez will make the start on Sunday against the D-backs at Marlins Park, and as of Friday, Richards is available in relief.

It's been a rough go for Richards for a while. In his last seven starts, the 26-year-old is 0-6 with a 7.32 ERA. On Monday, he allowed seven runs in five innings in a 9-1 loss at the White Sox.

“As an organization, we’re compiling starters,” Marlins manager Don Mattingly said. “Starters are getting closer and closer to the big leagues.”

In his second big league season, Richards had never pitched in relief, making 20 starts this year after 25 as a rookie in 2018. That changed on Friday, when he tossed a scoreless eighth inning while fanning two in Miami's 3-2 walk-off win over the D-backs.

Hernandez (1-4, 5.24) last started on July 4 at the Nationals, and he last pitched on July 20 at the Dodgers, giving up four runs in two-thirds of an inning.

As a starter, Hernandez is 1-3 with a 4.05 ERA. In 26 2/3 innings, he has 32 strikeouts and six walks.

For any of the Marlins’ young starters, the development of a third pitch is crucial to their sustainability in the rotation. Richards, for instance, has an above-average changeup, a pitch hitters are batting just .204 against. But he doesn’t have an overpowering fastball, and he’s yet to truly develop a consistent third pitch. Against his curveball, hitters are batting .407, and they’re batting .349 off his cut-fastball.

“The bullpen is obviously a little bit different,” Mattingly said. “Most guys out there are [throwing] two pitches, with a third in there somewhere. There are more two-pitch guys out of the bullpen.”

In his conversation with Richards, Mattingly said the message was for the right-hander to embrace a new opportunity.

“'Be open-minded to it,'” Mattingly said. “'We think it can be really good for you.' It could be good for us. It doesn’t mean he won’t be a starter again. But it’s something that we want to try.”

As for the long-range outlook, the Marlins have more starters coming through the organization. Sixto Sanchez, Miami's top prospect per MLB Pipeline, and No. 8 prospect Edward Cabrera are getting closer to being big league ready. Both are at Double-A Jacksonville.

Richards has five more years of club control, and the Marlins are open to trading some of their surplus pitching. Richards is the primary candidate to be dealt, while left-hander Caleb Smith is viewed as less likely.

If Richards isn’t dealt by Wednesday’s Trade Deadline, then he likely will stay in the bullpen for a while.

“These guys want to be in the big leagues, too,” Mattingly said. “Realistically, he hasn’t had the success. He’s had those pockets of success. But I don’t think we’ve seen a true, sustained rotation, or top-of-the-rotation type stuff at this point.”

Worth noting

• Pablo López (right shoulder strain) will make his first rehab assignment start on Sunday for Double-A Jacksonville, where he is scheduled to throw three innings or 45 pitches. Once built up to 90-100 pitches, Lopez will rejoin the rotation. That process could be several weeks away.

“He’s got to be built up as a starter,” Mattingly said. “He’s not going to be back at 60 pitches, and tax your ‘pen. We’ll get him built up to 90-100 pitches.”