The grime star was involved in a collision with a car in Bury, Greater Manchester.
Emergency services were called to the scene shortly before 9.20 pm.
Police did not confirm the identity of the injured man but told the people that the 29-year-old driver of the quad bike had been taken to hospital with serious injuries.
Videos apparently taken at the scene have been shared on social media.
The collision happened as the UK is in lockdown due to the coronavirus plague.
Fans and other artists have been sending messages of support to the rapper, real name Aaron Davis.
His condition is not believed to be life-threatening.
A deputy for Greater Manchester Police said: “Shortly before 9.20 pm last night,police were called to Rochdale Road, Bury to reports of a collision involving an Audi car and a quad bike.
“Emergency services attended and the driver of the quad bike – a 29-year-old man – was seriously injured and taken to hospital for treatment.
“His injuries are were life-threatening.”
Police have not made any arrests and say inquiries into the crash are ongoing.