Belgian rider Tom Boonen will miss the Tour de France because of a knee injury, his Quick Step team  announced on Friday.

The Belgian champion will also be unable to ride in Sunday's race at Louvain which he won last year.

The 29-year-old, injured last month in the Tour of California, was involved in a mass crash on the fourth stage of the Tour of Switzerland last week when he damaged his left knee.

"After three days of rest, I went out training yesterday (Thursday), about five hours on the Louvain route", said Boonen, who missed the 2008 Tour because of a cocaine problem.

"The pain in the knee was there the whole time. During the last hour of training, I had to stop several times. It is something that started after my fall in California and got worse after the fall in Switzerland.

"I am very disappointed for the team, the sponsors and the spectators particularly as the Tour is passing through Belgium.

The Belgian Quick Step team admitted it was a major blow: "It is terrible news for us," said team manager Patrick Lefevere who will name Boonen's replacement on Monday after the national championships.

Boonen has won six stages of the Tour de France and took the green jersey in the 2007 edition. The Tour begins on July 3 in Rotterdam and finishes in Paris on July 25.