Bjorg Lambrecht crashed after hitting a road reflector on stage three of the Tour of Poland, according to a prosecutor in Poland.
The 22-year-old Belgian rider died after he crashed 48km into the stage and hit a culvert, suffering serious internal injuries.
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Authorities in Rybnik, where Lambrecht fell, have launched an investigation into the cause of the crash, according to Belgian newspaper Het Nieuwsblad.
The deputy public prosecutor Malwina Pawela-Szendzielorz said: “Two riders who rode behind Lambrecht saw how he hit the reflector and lost control of his bike. He turned first to the right, then to the left, hit the road and hit the culvert.
“It is sad that reflectors, intended to improve road safety, are the cause of such a tragedy.”
The reflective road stud in Poland, used to separate lanes in darkness and bad weather, is 10 centimetres by 10 centimetres and sits 1.8 centimetres above the surface of the road.
Lotto-Soudal rider Lambrecht was resuscitated after the crash and was rushed to hospital, but the liver laceration he suffered caused an internal haemorrhage, which led to a cardiac arrest. He died during surgery.
The cycling world has been in shock since the death of the promising talent.
His funeral was held in his home village of Knesselare, where members of the public and his team-mates all attended to pay tribute.
Lambrecht was riding his second season at WorldTour level and had been one of the great Belgian hopes.
He finished second in the under-23 World Championships last year and went on to ride to 12th in the Critérium du Dauphiné, taking the youth classification in the process.
Lambrecht also finished fifth in Brabantse Pijl earlier this year, following up with sixth in Amstel Gold Race and fourth in Flèche Wallone.