Erik van Rooyen withdrew from the Masters with an undisclosed injury on Friday morning.
The 30-year-old South African was aggressively kneading his back over his final seven holes.
He will be replaced by familiar Masters marker Jeff Knox, an Augusta National Golf Club member who enters the field anytime an in-round change would leave a single golfer in a group.
With 94 players in the field, Knox was added to the field for the second round.
van Rooyen shot a 4-over 76 in the first round Thursday and was 5 over on his final five holes.
(Field Level Media)