Mullee underwent season-ending surgery to address a nerve issue in his elbow, LoHud.com reports.
Mullee was transferred to the 60-day DL earlier Saturday to clear up a roster spot, but it appears as though his season is now officially done. The 28-year-old, who is expected to be back at full health by the start of spring training, made his big league debut in 2016, posting a 3.00 ERA with four strikeouts in three innings. The righty was terrific in the minors though, working to a 0.99 ERA over 25 appearances with Triple-A Scranton/Wilkes-Barre, so he could get a shot to make the Opening Day roster in 2017.