Europe's aviation watchdog issued the notice, known as an emergency airworthiness directive, a week after the crash at the Clutha Vaults which killed 10 people, warning the problem was potentially disastrous if not treated. It affects both the Eurocopter EC135 models used by the emergency services in Scotland and its military version, the EC635. The defect relates to the ring frame, which links the fuselage to the tail rotor.
The European Aviation Safety Agency (Easa) said: "During a recent post-flight check, the pilot detected a crack which ran along three rivets across the ring frame.
"This condition, if not detected and corrected, would gradually reduce the structural integrity of the tail-boom fenestron attachment, potentially resulting, in the worst-case scenario, in detachment of the fenestron and consequent loss of the helicopter."
Easa has ordered operators to carry out inspections of the ring frame every 50 flying hours.
Aviation expert Chris Yates said the latest development was unlikely to be linked to the Glasgow crash, but added nothing could be ruled out, given previous alerts over cracks in the rotor hub area.
He said: "At this moment I don't think the issues we saw before are related to what happened in Glasgow, but I could be wrong. Nothing immediately jumps out, so investigators will be probing every nut and bolt. It remains to be seen whether cracks have anything to do with it."
An interim report by the Air Accidents Investigation Branch said there was no evidence of mechanical disruption to the engines which could explain why the police helicopter suddenly dropped out of the sky.
Bond Air Services advised its emergency service clients to ground Eurocopter EC135s earlier this week after it reported a technical fault on board an air ambulance in England.
The safety alert was lifted on Thursday, although some helicopters, including the Scottish Ambulance Service's air ambulance in Glasgow, are still undergoing safety checks.
However, Chief Superintendent Ian Whitehouse, chief operating officer of the National Police Air Service which operates police helicopters in England and Wales, did not ground its EC135s. He said they would continue to run, but would be loaded with more fuel than normal.
He added: "In the light of the technical issue identified by Bond, as a precautionary measure, we are increasing fuel levels on all NPAS EC135 aircraft and increasing the minimum level of fuel pilots are allowed to operate on."