De Los Santos is not listed on the Guardians' Opening Day roster, Zack Meisel of The Athletic reports.
The Guardians attempted to add left and right field to De Los Santos' defensive skill set this spring in an effort to make him easier to carry on the 26-man roster, but he will fail to make the cut after posting a .545 OPS across 44 spring plate appearances. The Guardians acquired De Los Santos via the Rule 5 Draft this offseason, so the 20-year-old prospect will now be offered back to the Diamondbacks and likely head to Double-A or Triple-A to begin the year.