Morikawa, who arrived at the PGA Tour's flagship event this week as one of the pre-tournament favourites, parred his opening hole at TPC Sawgrass, the par-four 10th, and then withdrew at the tee at the par-five 11th.
The two-time major champion took a practice swing at the 11th tee and then immediately reached for his back with his right arm. He then went to a golf cart, removed his hat and placed his arms on his head as he was taken from the course.
Morikawa won the AT&T Pebble Beach Pro-Am last month for his seventh PGA Tour victory and followed that with top-10 finishes at the Genesis Invitational and Arnold Palmer Invitational.