The president of the union at Spain's tax authority says he expects Real Madrid forward Cristiano Ronaldo to face charges in court over his financial arrangements, just as Lionel Messi had in the summer.

A group of European media outlets have reported that Portugal captain Ronaldo has directed at least €150 million in income through the British Virgin Islands tax haven since 2009, and that the Spanish tax authorities have been investigating his affairs for 12 months already.

The reports have also accused Manchester United manager Jose Mourinho and a number of other high-profile football figures of having used similar frameworks of overseas companies to avoid paying tax on income from image rights.

Both Ronaldo and Mourinho are represented by Jorge Mendes' agency Gestifute, which has strongly denied any wrongdoing and said all of its clients are fully compliant with their tax obligations. Mourinho has also said he has nothing to hide.

In July, Messi was found guilty of tax fraud and sentenced to 21 months in prison -- which he did not have to serve under Spanish law -- after it was found that he and his father had broken Spanish laws by using tax havens to hide image rights income.

On Monday, the Gestha union, which represents lower-level workers at the tax authority, released a statement saying the ongoing investigation into Ronaldo had showed evidence of serious tax offences that could merit a prison sentence.

Its president Carlos Cruzado was later asked on Cadena Ser's "El Larguero" radio show if Ronaldo would follow Messi in ending up in front of a judge to face tax fraud charges.

"That is what you would expect," Cruzado replied. "We feel that the tax authority should pass the case to the public prosecutor, so that they take the reins on this. It is very easy to see this ending up in front of a judge, for sure. We are all part of the tax authority, although sometimes people doubt this, especially when the papers are full of stories like this."

Jorge Mendes' Gestifute agency has strongly denied its clients are guilty of wrongdoing over their tax arrangements. Europa Press/Europa Press via Getty Images

In May 2016, Mourinho agreed a settlement of €2.1 million with the Spanish tax authorities to cover image rights income earned between 2010 and 2013, when he was Real Madrid manager, that had not been declared at the time. However, Messi and Barcelona teammate Javier Mascherano were both found guilty of a crime after prosecutors decided their cases should be heard by a judge.

Cruzado said that even those working within the tax authority were not sure of the exact criteria used to decide which cases are settled and which brought to court but that in his view he felt Ronaldo would be charged with an offence.

"It would be good to clear up the exact criteria," he said. "There can be cases which are very similar, dealing with tax havens, that are dealt with differently, but the end objective should be the same. In [Ronaldo's] case it seems there is evidence of an offence and we would think that soon the prosecutor will receive a notification from the tax office."

During an interview with La Voz de Galicia, Spain's Prime Minister, Mariano Rajoy, declined to comment on Ronaldo's tax.

"That is an issue for the Agencia Tributaria [Tax Authority] to get into," Rajoy, a Real Madrid fan, said. "I make sure not to comment about things I do not know."

Spain's Secretary of State for Tax Affairs, Jose Enrique Fernandez de Moya, has also said that the tax authority should be allowed to do its job without government interference or media pressure. The Spanish newspaper ABC reported that legal sources it consulted predict a case could drag on for 10 years if charges are brought against Ronaldo.

El Mundo, meanwhile, has reported that Madrid's Pepe and Fabio Coentrao, both also Gestifute clients, are being investigated for not having paid taxes on a combined €7m in image rights income.

The newspaper also said Madrid playmaker Luka Modric is being investigated over allegations his image rights income was moved to a Luxembourg-based company owned by his wife and established a few months after he signed for Madrid in 2012.