Sporting CP president Frederico Varandas has alleged that Porto officials attacked him and stole his phone and wallet after a 2-2 draw between the teams on Saturday.
Varandas said the incident happened outside the team bus, with Porto athletic director Rui Cerqueira ramming into him and taking his belongings.
The game itself was marred by a brawl between players.
What has been said?
"Sporting CP informs that the president Frederico Varandas was yesterday the target of verbal aggression and attempts of physical aggression by Vitor Baia, vice president and administrator of FC Porto, Sergio Conceicao, coach of the team, and Rui Cerqueira, club press director," wrote Sporting CP in a statement on their official club website.
"When [Varandas] was going to the team bus, the three men, surrounded by several security guards, made a wait for him. Then, Rui Cerqueira violently rammed the president, taking his wallet with mobile phone, personal identification cards and credit cards from his hand, immediately running away. Despite the presence of the police at the scene, the device and documents were not found.
"Sporting CP will file a criminal complaint against Vitor Baia, Sergio Conceicao and Rui Cerqueira. And it will make every effort to ensure that the aggressors of these acts are banned from sports venues.
"What happened yesterday, on and off the pitch, is too serious to have no consequences."
Porto have yet to issue an immediate response to the allegations.