New York Mets general manager Billy Eppler resigned Thursday amid a Major League Baseball investigation into his use of the so-called phantom injured list, sources told ESPN.

The practice of placing players on the IL with fake injuries is a long-accepted but ethically murky part of baseball, according to sources. Teams will ask players -- often struggling and on the fringe of a roster -- to accept an IL placement even when capable of playing, sources said. The player gains the benefit of service time, a major league salary and retaining a spot on the team's 40-man roster, while the team retains the player amid a potential 26-man roster crunch.