Two cyclists attacked the man following a dispute over parking on Castlebank Street, according to union bosses.
They say one of the brutes assaulted the victim at around 9.15pm on Sunday with a knuckle duster, leaving him with an eye injury.
A statement from union Private Hire and Taxi Monthly - the official newspaper of the National Private Hire Association - read: "Angry to report: another vicious attack on Glasgow driver.
"Private hire driver parked his car and did delivery when two cyclists verbally abuse him because of where he has parked but police had no issue with parking.
"One of the cyclists then attacks the driver with a knuckle duster."