London's Metropolitan Police Service said the injuries Watson and his aide had suffered were "not life-threatening".
The incident took place in Chingford, east of London on Thursday, according to a statement issued by London's Metropolitan Police Service on Saturday.
The statement said the injuries Watson and his aide had suffered were "not life-threatening".
Watson is one of the most popular figures in British boxing having survived life-threatening injuries in a career-ending 1991 defeat by domestic rival Chris Eubank when the pair met for the World Boxing Organisation super-middleweight title in London.
The Metropolitan Police statement said they were called at 1653 GMT Thursday, February 16 to reports of an attempted robbery on The Ridgeway in Chingford.
Two men, aged in their 50s, informed officers that they had been sprayed in the face with a "suspected noxious substance" by two suspects who attempted to steal the car.
However, the male suspects fled the scene in a different vehicle.
"The victims were assessed at the scene by the London Ambulance Service before being taken to an east London hospital for further treatment; their injuries are not life-threatening," the statement added.
There have been no arrests and enquiries continue.