The 32-year-old Englishman was due to face close friend and training partner Saurav Ghosal of India in the opening round but his withdrawal means that his spot in the main draw will now be taken up by Hong Kong’s Leo Au.

Willstrop finished as a runner-up in the event in 2012, losing to current champion Ramy Ashour of Egypt in the final.

The battle to fill the four remaining places at the men’s PSA World Series Finals is wide open heading into the El Gouna International.

Following last month’s British Open in Hull, several players have come into contention for a coveted berth at the season-ending tournament, which sees only the top eight players in the Road to Dubai standings come together in one of the sport's most lucrative events.

Only the top four players in the current rankings - Egyptians Mohamed Elshorbagy and Omar Mosaad, France’s Grégory Gaultier and England’s Nick Matthew - are assured of their places.

A dozen other players, including Ashour, Colombia’s Miguel Angel Rodriguez and Australia’s Cameron Pilley, are set to fight for the remaining spots in the Egyptian tourist resort from April 24 to 29.

Top seed Elshorbagy has been drawn against fellow Egyptian Mazen Hesham in the first round and will play Ashour in the quarter-finals if seedings go to plan.

The PSA World Series Finals are due to take place from May 24 to 28.

Players will initially compete in a round-robin format for a place in the semi-finals.

An equivalent women's competition will also be held.