CCTV footage shows the moment the Hollywood star ploughed into the bonnet of the Mercedes estate car on Tuesday.
The Ocean's Eleven actor's helmet smashed the car's windscreen as he was flung into the air before landing on the ground.
Italian news agency ANSA quoted driver Antonello Viglino as saying he was "stationary on the roadway" and ready to turn left when two motorcycles came from the other direction.
Mr Viglino says the first, thought to be Clooney's bodyguard, "avoided collision" but the second "slammed into me".
The 67-year-old told the Corriere della Sera newspaper that he had just slightly moved into the opposite lane, adding: "I didn't see anything, I had the sun in my eyes."
Clooney was treated and released from Olbia Hospital on the island.
A spokesman said: "He is recovering at his home and will be fine."
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The actor is in Sardinia filming Catch 22, a television adaptation of Joseph Heller's book of the same name.
The miniseries will be his first television role since 2009, when he made his last appearance as Dr Doug Ross on ER.