Athletics pitcher Jarrod Parker suffered a fractured medial epicondyle, the bone that anchors the Tommy John graft in his elbow, according to Bay Area News Group.

Parker suffered the injury while throwing a pitch during his rehab start on Friday. He immediately went to the ground, grabbing at his arm after a pitch went flying past the catcher. It is unclear if Parker will need to undergo a second Tommy John surgery to repair the damage done. Athletics trainer Nick Paparesta said Parker will need surgery, but it's not clear yet how much.

Parker was working his way back from the surgery he underwent last March.