Los Angeles - Australia's Jason Day withdrew from Wednesday's pro-am on the eve of the US PGA Tour Farmers Insurance Open because of flu-like symptoms, casting doubt upon his Torrey Pines title defense.
Day won a playoff last year at the San Diego layout for his third PGA title and his first in a breakout season that saw him win five times, including his first major crown at the PGA Championship, and claim the world number one ranking for the first time in his career.
"Looking forward to getting back under way and trying to defend this tournament, which is very special to me," Day said earlier. "That kind of catapulted my year to turning the way it did."
Day is set to play alongside Americans Harris English and J.B. Holmes in the first two rounds. The trio and American Scott Stallings were all part of last year's playoff, which Day won with a par on the second extra hole.
Five-time major champion Phil Mickelson, who shared third last week, is a treble past Torrey Pines winner who lives nearby. He plays alongside US compatriot Jimmy Walker and England's Justin Rose, who has been off for nearly two months.
Mickelson has not won at Torrey Pines since 2001 and has not won any title since the 2013 British Open.
Day would become the fourth back-to-back Torrey Pines champion with a victory this week, matching J.C. Snead from 1975-76, Phil Mickelson in 2000-01 and Tiger Woods, who had a record four wins in a row from 2005-2008.
American Rickie Fowler, coming off a victory in Abu Dhabi, is paired alongside Japan's Hideki Matsuyama and American Patrick Reed.
"The ultimate goal this year is to go win a major and this is a step in the right direction for sure," Fowler said after his Abu Dhabi triumph.
World number four Fowler hopes to capture his first major title this season, perhaps following Day's formula by doing it after a Torrey Pines title.
"With where my game's at, the best it has been this early in the season in my career, I'm working on getting ready for Augusta. And I'd like to have my shot at getting the green jacket there."
Australian 17-year-old Ryan Ruffels will make his professional debut in the event.