The Padres placed Waldron (lower body) on the 15-day injured list Wednesday.
Waldron, who underwent hemorrhoid surgery in late February, is still in the process of getting built back up again and isn't expected to be ready to return from the IL until around mid-April at the earliest, per MLB.com. Waldron was able to pitch in two Cactus League games before the end of spring training, so he could be cleared to head out on a rehab assignment with Triple-A El Paso in the near future.