The incident took place with just over 185 kilometers to go in the 212-kilometer stage with cameras only focussing on De Marchi as medical teams rushed to his aid at the side of the road.
He was put on a stretcher before being transported to hospital. Earlier in the stage, De Marchi had been on the attack and was a prominent figure in trying to establish a breakaway. It appears that he was the only rider to come down in the fall.
De Marchi finished second on stage 4 of the race and wore the maglia rosa for one day.
Having earlier stated that De Marchi avoided a head injury and was conscious after the fall, Israel Start-Up Nation later released an update detailing the Italian's injuries.
The 35-year-old has suffered a broken collarbone, six broken ribs and two vertebrae as a result of the crash.
"Dema was taken to hospital and was diagnosed with a broken right collarbone and six broken ribs," the statement read. "He also broke his first and second thoracic vertebra.
"He did not suffer any head injury, but does have to stay in hospital for at least one night."
De Marchi suffered a similar exit from the 2019 Tour de France, riding for CCC, crashing out on stage 9 and suffering a head wound as well as broken collarbone, ribs, and a collapsed lung.
The Italian wasn't the only Israel Start-Up Nation rider to leave the Giro on stage 12, with Alex Dowsett climbing off with 150km to go after suffering from stomach problems.
De Marchi update:Dema was taken to hospital and was diagnosed with a broken right collarbone and six broken ribs. He also broke his first and second thoracic vertebra.He did not suffer any head injury, but does have to stay in the hospital for at least one night.#Giro pic.twitter.com/E7rNagn752May 20, 2021
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