Security has slipped deeper into farce after a second bullet is understood to have been fired at the Olympic equestrian venue.
Officials said that no one had been hurt in an 'incident' at the stable area, housing horses worth millions of pounds.
It came only four days after a bullet passed through the tented roof of the equestrian media centre, landing just two metres from a photographer.
That first bullet was initially believed to have come from nearby army live-fire exercises, though Rio 2016 claimed that it was fired by a local at a police blimp from a nearby favela.
Rio 2016 were at pains to dismiss that as a freak occurrence with 'no risk' of a repeat but the latest episode will cause alarm.
It came a day after Tuesday's attack on an official media bus with claims that its windows were shattered by gunfire. Officials insist the damage was done by rocks.