It happened near Central Avenue and San Bernardino Street on Feb. 16.
Police say the victim was taking money out of an ATM when he was attacked.
The victim was sent to the hospital where he was treated for a brain bleed, authorities said. The suspect reportedly took his money and wallet.
The suspect, described by police only as a white male with a red beard, was last seen driving a silver or tan Chevrolet Silverado, possibly with a California handicap license plate.
Anyone with information is urged to contact the Montclair Police Department at 909-621-4771.