The pensioner was crossing Argyle Street at its junction with Jamaica Street when he was struck by a bus at about 19:10 on Saturday.
He was taken by ambulance to Glasgow Royal Infirmary where he is being treated for a head injury.
Police appealed for witnesses to the crash to come forward.
An 80-year-old man who was hit by a bus in the centre of Glasgow is in a critical condition in hospital, police have said.