Cycling great Eddy Merckx sustained head injuries in a crash while riding with friends.
Belgian newspaper the Het Nieuwsblad newspaper said the 74-year-old Merckx crashed on Sunday and was admitted to a hospital in Dendermonde.
Merckx is regarded by many as the greatest cyclist ever.
He who won five Tour de France titles and a record 34 stages.
The 2019 Tour de France began in Brussels in July and feted Merckx to mark the 50th anniversary of his first Tour victory.
Known as The Cannibal for his appetite for winning, Merckx also won five Giro d’Italia titles, one Spanish Vuelta and a string of one-day classic races.
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