The warning comes after two high-profile sport stars were robbed by gangs as tourists prepare to flock to the Spanish paradises this summer.
Sampdoria footballer Cristiano Piccini had his luxury watch stolen in Ibiza.
Motorbike muggers tried to run him and his wife over in front of their children in a terrifying broad daylight attack.
Argentinian tennis star Federico Coria also had valuables including his rackets, laptop and engagement ring taken from him in Barcelona.
Piccini was targeted in upmarket Marina Botafoch in Ibiza Town near a well-known hotel.
The 31-year-old defender said on social media: “Hello I’m writing to warn you so what happened to me doesn’t happen to you.
“I was walking in Botafoch Marina in front of the Ibiza Gran Hotel with my wife and my two children at 3.15 in the afternoon.
“I was assaulted by two people, two Italians and from the accent I’m pretty sure they were Neapolitans.
“They caught me from behind and stole my watch, I reacted quickly, I managed to get to the thief, who was leaving on a motorbike that was waiting for him on the other side of the pavement.”
Saying the motorbike rider had tried to run his wife over, the footballer added: “Obviously the most important thing is that my family and I are okay.
“What pains me is that this island, which is like my second home, is full of this sort of scum who without a second thought mug people like this, with children and family there.”
He went on to claim he had received no help from onlookers, warning tourists: “If you’re thinking of coming to Ibiza, be careful about what you wear, because of the way things are here, as you can experience a very unpleasant moment.”
Taking to TikTok, Coria revealed his own experience of becoming another Barcelona crime statistic.
The 32-year-old said how he and his girlfriend were targeted in a car park at Barcelona Airport.
He said: “My girlfriend saw something and went towards the luggage trolleys at the front of the car and saw a person running away with some of our suitcases.
“I was on the back seat of the car and heard her shouting but didn’t understand anything.
“When I got out I saw her running behind the man.
“In my desperation I didn’t close the vehicle and another person took the rucksack where there was a laptop and other technology and my engagement ring.”
He added: ”We went to report the crime to the airport police. We’d come from Paris which we know is dangerous and where you have to have your wits about you, but in an airport with so many cameras I would never have imagined this sort of thing was so common in Barcelona.
“There were two other people who had been robbed.
“I wanted to do this video to be able to alert people who are in Barcelona so this doesn’t happen to them.”
He finished up by saying: “It’s sad that they have all these cameras and police can’t do anything without judicial authorisation.
“They tell you the person who steals has more rights than the victims.”
The two sportsmen have gone public with their warnings as British and Irish tourists prepare to flock to Spain this summer.
Both Ibiza and Barcelona are known as favourite places for Rolex robbers who target holidaymakers.
Late last month two moped muggers were filmed snatching a man’s watch off his wrist in heavy traffic near Ibiza airport.
The pair took advantage of cars approaching a roundabout on the road to the airport ground to a halt to commit their crime.
Footage showed the moped rider approaching the driver’s window before his accomplice, who got off the vehicle as they prepared to pounce, rushed over to complete the snatch with his motorcycle helmet still on his head.
They were away seconds later, accelerating at speed in the direction they had come from, before other motorists had a chance to react.
The man they targeted, who was driving a luxury Mercedes G-wagon, tried to do a U-turn to follow them but appeared to give up after realising he had no chance of catching up with them.
The footage emerged hours after police on the island were pictured returning a £35,000 watch stolen by criminals to its rightful owner.
Detectives said it was one of seven expensive timepieces they had recovered after arresting the suspects.
A day earlier a gang of Rolex robbers pleaded guilty to targeting tourists in Majorca.
The five criminals accepted prison sentences ranging from three months to five years after admitting they had travelled to the island from Barcelona between March and April last year to commit crime.
They mugged four victims to snatch watches worth nearly £150,000 in total.
One was a French tourist wearing a £85,000 Audemars Piguet watch.
They also targeted a woman wearing a £42,000 Rolex white gold watch in an underground car park in Palma.