The Air Canada flight from Montreal lost its wheel as it taxied down the runway before take-off but the pilot is believed to have continued with the flight without noticing.
The plane, carrying almost 300 people, then arrived at Heathrow with one of the rear tyres missing but somehow managed to land without any complications.
An Air Canada spokesman said the wheel is believed to have fallen off the bearing on the runway in Montreal.
A shocked Heathrow worker told The Sun: “I’ve never seen anything like this in my life.
“There is no way the plane would have taken off in Canada without someone doing the final checks on it and they would have noticed if a wheel was missing.
“The proper checks could not have been carried out because these wheels are worth around £10,000 each and they don’t simply just fall off.
“None of the passengers knew what had happened and neither did the pilot, he was in shock when he landed and was told about the wheel.”
The plane is now grounded at Heathrow while it is inspected and repaired.
A spokesman for Air Canada told the newspaper: “Preliminary information indicates that a wheel separated from the aircraft while taxiing down the runway before take-off in Montreal and came to rest beside the runway.
“As the landing gear is comprised of 8 wheels, this had no impact on the safe operation of the flight.
“Flight AC864 an A330 with 294 passengers on board landed normally in London and taxied to the gate.
“Passengers on the returning flight are being re-booked on other flights later today while the aircraft is being repaired.”