Polish news website Onet reported Lambrecht collided with a concrete structure around 30 kilometres into the race after it suddenly began to rain.
One rider anonymously told reporters Lambrecht had his arms raised calling for a cycling director moments before the crash.
Lambrecht had been promoted to Lotto Soudal's senior setup a year ago having shown potential for their Under-23s team.
Race organisers added: "There are no words to describe this tragedy".
But his team confirmed he passed away on Monday.
Throughout the day pro teams and riders took to social media to mourn Lambrecht and to offer their condolences to his friends and family.
In 2017 he won the U23 Liege-Bastogne-Liege cycle, and was also second in other races in the same category such as the Tour de l'Avenir, the Tour de Savoie Mont-Blanc and the Giro della Valle d'Aosta. So young with so many things yet to do.
Lambrecht's accident on the Tour de Pologne was followed by several more on the Chorzow to Zabrze stage, none of which were fatal.
"The injuries were so serious that we called for a helicopter and an ambulance".