Mariners general manager Jerry Dipoto said Haniger had microdiscectomy surgery to make a small repair to a vertebrae, according to Ryan Divish of the Seattle Times.
Haniger's start to the 2020 season will be delayed significantly, though an exact timetable for his return remains unclear, Jeff Passan of ESPN reports.
The 29-year-old suffered a setback in January while rehabbing a ruptured testicle, which resulted in the core procedure. He was initially expected to miss six-to-eight weeks.
Haniger hit .220/.314/.463 with 15 homers across 63 contests before going down with the testicle injury and a subsequent back ailment that kept him out for the rest of the 2019 campaign.
The former All-Star had a career year in 2018 when he posted an .859 OPS with 26 round-trippers and 93 RBIs for the Mariners.