Seoul - South Korean police raided a sports agency as part of a fraud inquiry after Juventus superstar Cristiano Ronaldo sat out a friendly in Seoul, enraging thousands of fans.

Police said the raid, which followed a criminal complaint, was intended to investigate whether whether the agency lied by claiming Ronaldo was guaranteed to play.

"We raided the office on Thursday," a Seoul police officer told AFP.

"We are looking into whether the agency proceeded with the match even though they were well aware prior to the game that Ronaldo may not -- or was not going to -- play."

A criminal complaint filed by an unnamed individual accuses agency The Fasta of swindling some 6 billion won (US$4.9 million) worth of ticket sales by saying the contract with the Italian club obliged Ronaldo to play for at least 45 minutes, and not warning buyers that he might not appear.

The Portuguese striker stayed on the bench throughout last month's friendly against a K-League all-stars team, with Juventus saying he was rested on medical advice because of muscle fatigue.

The sell-out 65,000 crowd made its displeasure known during the game, which was delayed for an hour after Juventus arrived late from the airport.

The K-League has accused Juventus of "deception" and demanded an apology.

But the club has rejected accusations of deception and misbehaviour, with chairman Andrea Agnelli writing to the K-League: "Ronaldo was... obliged, according to our medical staff's advice, to rest due to a muscle fatigue.

"I definitely reject your accusation of irresponsible behaviour, arrogance, of disregard for fans, which we always honour," he added.

The head of The Fasta, Robin Jang, has been banned from leaving the country and will soon be questioned, police added.