The 30-year-old Hawthorn man was riding in the Melbourne suburb of Abbotsford at midnight last night when he was involved in the horror crash.
He is believed to have crashed into the street sweeper and fallen off his bike, causing him to become trapped underneath the heavy machine.
The 30-year-old was rushed to hospital with life-threatening injuries.
The driver of the street sweeper, who was unhurt, stopped at the scene to assist.
Police are appealing for anyone who witnessed the incident to contact Crime Stoppers on 1800 333 000.