UEFA president Aleksander Ceferin has admitted "weak" aspects of Financial Fair Play (FFP) rules require review to prevent loopholes from being exploited.

Calls for action to be taken against Manchester City and Paris Saint-Germain have made been in the wake of allegations from Der Spiegel and Mediapart that the clubs circumvented FFP spending stipulations.

Premier League champions City declined to comment on the reporting - purportedly informed by documents obtained from whistleblowers Football Leaks - adding only that "the attempt to damage the club's reputation is organised and clear".

PSG maintained that they have "always acted in absolute compliance with the laws and regulations issued by sports institutions".

Ceferin stopped short of commenting on the heavyweights in question but conceded moves must be made to address FFP vulnerabilities.

"I don't want to speak about Man City or PSG but for any club the rules have to be strong and clear," Ceferin told BBC Sport.

"We will act by the book, by the regulations.

"We know that we have to modernise. We know we have to check the rules and regulations all the time. We know that the situation in the football market is changing all the time.

"So that's also part of our thinking for the future - do we have to do something about the regulations to be more robust? Yes."

LaLiga president Javier Tebas has encouraged UEFA to impose Champions League bans on City and PSG as a means of sending a message.

Ceferin confirmed all possible deterrents had been discussed, adding: "It's the start of the debate. It's a bit premature to speak about it but we acknowledge the rules might be weak in certain points.

"Also laws in certain countries are changing all the time [and] adapting to modern times."