Right-hander Zack Burdi was also designated for assignment by the Dodgers to make room on their 40-man roster.
Vanasco, a 15th-round draft pick out of Texas in 2017, was designated for assignment Monday. He allowed six runs in 2⅓ innings in two games for Double-A Frisco after being activated from the injured list. Vanasco was 3-5 with a 4.68 ERA in 23 starts between Frisco and High-A Hickory.
The 19-year-old Valdez was 0-2 with a 3.12 ERA in eight games for Low-A Rancho Cucamonga this season. He was signed by the Dodgers as a minor league free agent out of Mexico in 2019.