A saddle sore stopped him riding the Tour of Denmark last week and the problem is continuing to affect Boonen's ability to train. He is having treatment but it is now unclear when he will return to racing. Boonen did not ride the Tour de France and then abandoned the Tour of Austria due to the flu. He won stage two at the Tour de Wallonie on July 21 but has not raced since then.
"I'm really disappointed. I really like the Eneco Tour and it's too bad I can't be at the starting line, but right now it's essential that I take the proper time to heal from this cyst, which is preventing me from training consistently and which I don't want to underestimate," Boonen said in statement from the Omega Pharma-Quick Step team.
"I have to say 2013 has definitely not been my year. Now the goal is to get better and get back to the races in the month of September, even though as things are now we can't really set any definite date for a return."
In 2012 Boonen became the first rider to complete the Tour of Flanders and Paris-Roubaix double for a second time, and he also became the only rider to win those two races plus Gent-Wevelgem and the E3 Harelbeke in the same year.
His 2013 season has been a disaster and he has only won two races: the minor Heistse Pijl race and the Tour de Wallonie stage.
During the winter Boonen was struck by such a severe case of food poisoning that he ended up in hospital in December. He was back in the ward again in January with a severely infected wound on his elbow. A crash at Gent-Wevelgem and then another at the Tour of Flanders knocked Boonen out of Paris-Roubaix. He returned to earn a few top finishes at the Tour of Belgium in May before falling victim to the flu in early July.
Mark Cavendish replaced Boonen at the Tour of Denmark and won the final stage. However he is now enjoying a well-deserved break and will not race again until the Tour of Britain.
Omega Pharma-Quick Step has yet to name its squad for the Eneco Tour but Alessandro Petacchi is set to be make his return to professional racing in the week-long stage race.