Andrei Kivilev has died from head injuries suffered in a crash during the second stage of the Paris-Nice race.
Kivilev was left in a coma after a crash in Tuesday's stage
The Kazakh rider's Cofidis team made the announcement on Wednesday, one day after a horrific crash near the French town of St Etienne put him in a coma.
Kivilev, who had not been wearing a helmet at the time of the accident, underwent surgery at a St-Etienne hospital, but his condition worsened overnight.
The 29-year-old is the first elite cyclist to be killed since Spainiard Manuel Sanroma, who crashed in the 1999 Tour of Catalonia.
Andrei Kivilev fact file
Born: 21/09/73 in Kazakhstan
Teams: Festina (98/99), AG2R (00), Cofidis (01/03)
Highlights: Won 2001 Route du Sud, 4th in 2001 Tour de France, 4th in 2002 Paris-Nice
World ranking: 50
Tour de France champion Lance Armstrong was among those who paid tribute to Kivilev.
"I came to know Andrei quite well over the years and really
admired him and his style," said the American.
"I loved to race with him because you knew when he was in the race, and when the road went uphill, he would lay it all out.
"He helped me more then he or anyone will ever know -- and now he's gone."
A strong climber, Kivilev turned professional in 1998 and finished fourth in the 2001 Tour de France.
His priority this year was to help British team-mate David Millar in Le Tour.
Cofidis will continue to compete in the Paris-Nice race which finishes on Sunday.
But team director Francis Van Londerseele expressed his deep shock at the tragedy on Tuesday night.
"We're all shocked. Our thoughts have now turned towards his wife Natalie and their young son Leonard.
"This accident reminds us just how dangerous this sport is. We all regret the fact that Andrei was not wearing a helmet at the time of this fall."
The fact that Kivilev was not wearing a helmet looks set to spark safety debates.
Cofidis team doctor Jean-Jacques Menuet confirmed that a helmet would probably have saved Kivilev's life and called for the authorities to bring in stiffer safety measures.
"The injury Andrei sustained on his skull is located at a point that would have been protected by a helmet," said Meunet.
"Riders are free to wear a helmet or not, even though as doctors we would all like to see it become obligatory."
Cycling's ruling body, the International Cycling Union, tried to make helmets obligatory in 1991, but cyclists staged an angry protest and a compromise was reached forcing riders to wear helmets in certain conditions.