Hideki Matsuyama withdrew during Friday's second round of the Valero Texas Open with a neck injury.
There was no immediate word on his status for next week's Masters, where he is the defending champion.
Matsuyama, 30, carded a 2-over 74 in the first round Thursday in San Antonio. He withdrew Friday after playing nine holes in 1-under 35.
Ranked #12 in the Official World Golf Ranking, Matsuyama has not completed a tournament since he tied for 20th at the March 3-6 Arnold Palmer Invitational. He withdrew from The Players Championship (March 10-14) due to a back injury.
He has two wins on the PGA Tour this season at the Sony Open in Hawaii in January and the ZOZO Championship in Japan in October.
Last April at Augusta National Golf Club, Matsuyama defeated Will Zalatoris by one stroke to win the Masters and become the first man from Japan to win a major.