Toronto police are investigating following an early-morning incident that cost a cyclist his leg and has him fighting for his life.

The incident occurred at the intersection of Dovercourt Road and Argyle Street at 2:30 a.m. on Friday.

Witnesses say they heard shouting, possibly an argument, then a crash.

Police suspect a taxi backed into the cyclist, pinning him against a utility pole and crushing his leg. Sgt. Tim Burrows of Toronto Police Service's traffic division told ctvtoronto.ca the man has "critical injuries to the lower extremities."

Doctors amputated the 36-year-old man's right leg. The victim is still in critical condition, he said.

The Beck taxi cab had left the scene when police arrived. Three hours later, the taxi driver called police, Burrows said.

Police found the cab at a Benjamin Boakes Trail address, which is in the Keele Street and Sheppard Avenue area.

The driver admitted hitting the cyclist, but claimed "some type of altercation" occurred first, he said.

"He has been co-operative with us and has talked to investigators," Burrows said.

The man has not been arrested or charged, and the investigation is ongoing, he said.