The Marlins selected De Los Santos' contract from Triple-A Jacksonville on Tuesday, Christina De Nicola of MLB.com reports.
De Los Santos was named the Texas League Player of the Month for April after leading the circuit with 32 hits, seven home runs and 58 total bases for Double-Amarillo, Alex Weiner of Arizona Sports reports.
De Los Santos cleared waivers Saturday and was returned to the Diamondbacks, Nick Piecoro of The Arizona Republic reports.
De Los Santos is not listed on the Guardians' Opening Day roster, Zack Meisel of The Athletic reports.
De Los Santos has been working out in both corner outfield spots this spring, Jason Lloyd of The Athletic reports.
The Guardians selected De Los Santos during the 2023 Rule 5 Draft on Wednesday.