Belgian rider Tom Boonen on Thursday underwent an operation on his injured knee that had ruled him out of the ongoing Tour de France.

His Quickstep team said the Belgian champion “underwent an operation to his left knee for a lesion in a pre-patellar band”.

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 month.

And he admitted that the operation had been a last resort.

“Last Friday I started training and the pain seemed to be diminishing,” he said. “On Monday I tried to do 100 kilometres and the situation immediately got worse.

“After consulting with the team’s medical staff and with Dr Claes we decided to go ahead with the operation.

“I’m calm and confident even though I’ll have to stay off a bike for a while. It’s the first time I’ve faced an injury of this type but I’m ready to work on recuperating as best as possible and get back to racing after observing the recommended recovery time.”

Team doctor Yvan Van Mol added: “After trying to heal Tom’s knee with a series of non-invasive targeted therapies, the operation was a necessary choice.

“Tom will have to rest for at least three to four weeks before gradually going back to training and eventually getting back into competition. At this time we cannot determine when Tom will be able to return to competition.”