French world squash number one Gregory Gaultier has withdrawn from this week's Oracle NetSuite Open in San Francisco due to an ankle injury.
The 34-year-old, who has won the event three times, was seeded first for the Professional Squash Association (PSA) M100 tournament.
However his ankle injury - a reoccurrence of the one that saw him pull out of last year's Men's World Championship at the semi-final stage - will prevent him from defending the title he won a year ago.
Gaultier is a former world champion, winning the global title in 2015.
As a result of his injury, Egypt's reigning world champion Karim Abdel Gawad is the new top seed and will play Faraz Khan of the United States in round one.
Mohamed Elshorbagy of Egypt moves up from third seed to number two and will take on a qualifier, while James Willstrop of England will now face a qualifier instead of Australia's Ryan Cuskelly, who has become the number eight seed.
Mexico's world number 21 Cesar Salazar moves into the main draw and will take on Cuskelly for a place in the quarter-finals.
The main draw is due to begin tomorrow with the tournament running until September 30.
Earlier rounds are taking place at local clubs, with the Justin Herman Plaza hosting from the quarter-finals onwards.