Riis admitted to using EPO between 1993 and 1998

The Dane, 43, admitted in May to using banned substances during his 1996 Tour victory and was subsequently erased from the race's list of winners.

"It was an extremely difficult decision to make," he said in a statement.

"However, it is my decision and I have not been pressed to make it. I feel I do not have the strength to help my riders throughout the Tour de France."

Riis, who said he used EPO from 1993-98, recently received the backing of team sponsors CSC, who said he had helped launch their rigorous anti-doping programme.

Riis had been due to arrive in London on Thursday for this year's Tour.

Tour director Christian Prudhomme last week declined to comment when asked if the Dane would be welcome.