Verstappen had closed rapidly on Grosjean's Lotus in what was a battle for 10th in the closing stages of the race. On lap 64, however, the Dutchman hit the back of Grosjean's E23 Hybrid under braking for Ste Devote, the collision sending Verstappen spearing into the barriers and bringing out the safety car.
While thankfully unhurt, Verstappen was held responsible for the crash by the stewards and will therefore drop five places from wherever he qualifies in Montreal in a fortnight's time. The 17-year-old Dutchman was also handed two penalty points on his Super Licence.
Grosjean lost out on a potential points finish as a result of the clash - he was pitched into a spin, from which he recovered to claim 12th at the chequered flag.
The incident also had far-reaching consequences at the front of the race, with Mercedes wrongly opting to pit race leader Lewis Hamilton during the safety-car period, effectively costing the Briton victory. His team mate Nico Rosberg triumphed instead, with Hamilton also dropping behind the Ferrari of Sebastian Vettel.