Paramedics were called to the scene on Cougar Court at 11:35 a.m.
They say the vehicle struck a pole.
The elderly man was taken to a trauma centre. A second patient suffered minor injuries in the same crash, police say.
The TTC says that its 102 Markham Road buses are diverting southbound along Lawrence Avenue East, Bellamy Road, Eglinton Avenue East and Mason Road.