Formula One driver Jenson Button and his wife Jessica were allegedly gassed in their sleep by burglars who raided their room as they lay unconscious.
The pair were staying with friends in a villa in St Tropez on the French Riviera when thieves broke into the villa after reportedly pumping anaesthetic gas into the property through its air conditioning vents.
They stole valuables worth more than £300,000, including his wife's £250,000 engagement ring.
Police in St Tropez confirmed they were investigating and are awaiting blood tests from the group.
Philippe Guemas, deputy prosecutor in Draguignan, told Europe1 radio: "To our knowledge there has never been a burglary like this in St Tropez where gas was used to knock out the victims.
"Nothing has been established. Jenson Button's entourage has made this claim as the driver didn't feel well the following day.
"We have taken blood samples which will be analysed."
A source close to Button insisted officers had told them there had been previous incidents of people being gassed by thieves in the area.
"That's what we were told by the police," he said, and added that the comments were "surprising and confusing".
Police reportedly suspect a pair of criminals carried out the raid after staking out the property where Button was staying for days beforehand.
"The burglars were in the same room as him and Jessica, rifling through all their drawers," a source told The Sun.
"But they weren't disturbed at all because the effects of the gas gives the burglars free rein."
He added: "The first they were aware was when they woke up groggy the next morning and realised the house had been turned upside down."
The group were unharmed but have been left "unsurprisingly shaken by the events", a spokesman for Button said.
"Jenson, Jessica and friends were on holiday in a rented villa in St Tropez when on Monday evening two men broke into the property whilst they all slept and stole a number of items of jewellery including, most upsettingly, Jessica's engagement ring," he added.
"The police have indicated that this has become a growing problem in the region, with perpetrators going so far as to gas their proposed victims through the air conditioning units before breaking in."
The ring is reportedly five carats with a large teardrop diamond set in a diamond-encrusted platinum band.
Button, from Somerset, who drives for McLaren Honda, married his model wife in Hawaii in December.
It has been reported that the 35-year-old F1 driver will join Chris Evans as co-host on the newly reinvented BBC motoring show Top Gear, after the departure of Jeremy Clarkson, Richard Hammond and James May.
The investigation into tracking down the burglars is said to be centred on CCTV footage from the area.
St Tropez in the south of France has long been a popular destination for the rich and famous.
It is not the first time gas has been mentioned in reference to a burglary in a wealthy area of the country.
In 2006 footballer Patrick Vieira, his wife and daughter were the victims of a raid on their family home near Cannes.
The family complained of feeling unwell after the burglary and it was later confirmed gas had been pumped into the air conditioning system of the house to keep them asleep while jewellery was stolen.