The Diamondbacks optioned Rojas to Triple-A Reno after Sunday's game with the Cleveland Guardians and recalled outfielder Alek Thomas from Reno on Monday.
Rojas, who turns 29 on June 30, was batting .235 with no homers and 26 RBIs in 57 games while primarily playing third base. He had an OPS of .607, down from .739 in 2022 and .752 in 2021.
Since the start of May, Rojas has batted .188.
"I think he was just a far cry from the player he was, and that's what I explained to him," Diamondbacks manager Torey Lovullo said before Monday's 9-1 win at Milwaukee. "I said, 'You're going to go down, get on your feet again, hopefully get 40-60 very consistent at-bats, get some rhythm to your swing, get a feel for the game and come back up here and help us win.'"
Lovullo said Rojas had been working on some mechanical adjustments at the plate but noted that it hadn't paid off in his results. Rojas had made over 500 plate appearances for the Diamondbacks in 2021 and 2022.
"One thing I told him is, 'Our best team, our best 26, has you on it,'" Lovullo said. "But not at the pace, how you're playing right now, that's not going to help anybody. He understood. He was disappointed. He understood."
Lovullo said Emmanuel Rivera's progress also played a role in the decision. Rivera is batting .313 with one homer and 18 RBIs in 38 games, primarily at third base.
Thomas, 23, has batted .195 with a .252 on-base percentage, two homers and 10 RBIs in 39 games with Arizona this season but made progress after getting sent to the minors. Thomas hit .348 with a .409 on-base percentage, .518 slugging percentage, three homers and 31 RBIs in 26 games with Reno.
The Diamondbacks lead the National League West even though Rojas, Thomas and outfielder Jake McCarthy all have spent time in the minors this season after appearing in at least 99 games for Arizona last year. McCarthy was recalled last month after an early-season slump sent him to Reno.
"If you told me that at the beginning of the year and we'd be  games above .500, I'd tell you you're probably drinking too much wine, too much red wine, [and] I am too," Lovullo said. "It just goes to show you anything is possible in this game, because guys have emerged."