A 35-year-old cyclist was critically injured when a tractor-trailer struck him in Brooklyn Tuesday morning, authorities said.

The man was riding down Jay Street when a truck traveling in the same direction attempted to make a right-hand turn onto Tillary Street and struck him around 7:15 a.m.

“As I was biking to Manhattan I saw the immediate aftermath of bicyclist hit by a semi-truck,” said a woman who came upon the scene shortly after it happened.

“Spread across three lanes was muscle tissue, pools of blood and a few red smears; a helmet resting beside a towel soaked with blood. The cop told me he’ll live, but he lost both of his legs,” she said.

The man was rushed to Methodist Hospital in critical condition.

The driver of the truck remained at the scene and has not been charged with a crime.