The ongoing Club World Cup is being used as a trial run for another potential refereeing revolution in football, with fans in the stadium able to hear officials explain decisions taken following VAR reviews.

Referees being hooked up with microphones is nothing new in other sports such as the NFL, but it is only now being tested in football, just as the sport is still getting used to Video Assistant Referees and semi-automated offside technology.

And so Uruguayan referee Andres Matonte was able to succinctly explain why he awarded a late penalty to Real Madrid after coming across to review a possible foul in the box during the Spanish club's 4-1 win over Al Ahly in the semi-final in Rabat on Wednesday.

"Penalty decision, foul by number 17", Matonte told spectators on looking at the challenge by Al Ahly's Amr El Solia on Real forward Vinicius Junior. Luka Modric's kick was then saved.

Matonte's exchanges with the Video Assistant Referee remained confidential, but his brief announcement was relayed over loudspeakers in the stadium, to the delight of the crowd, with the majority of fans backing the European champions.

The International Football Association Board, the sport's lawmakers, approved the trial last month with English FA chief executive Mark Bullingham -- who sits on the board -- saying it was "important in terms of transparency".

FIFA are considering further trials at the Under-20 World Cup, scheduled to take place in Indonesia in May and June.

If deemed successful, the system may be given the green light for the Women's World Cup in Australia and New Zealand in July and August.

"I hope the spectators will benefit from this," said Pierluigi Collina, the chairman of FIFA's referees committee.

"We are at the beginning, it's the first time we're doing it, so certainly it might not be perfect...but I'm confident that the outcome will be positive."