The Barcelona star's father has discussed the ongoing legal battle between his former club and his current employers

Neymar's father has accused Santos' owners of having "mental diarrhoea" after they lodged a formal complaint against him and Barcelona to Fifa.

The Brazilian side claim the father of the Brazil captain and the Catalans opened negotiations over his move to Camp Nou two years ago without their permission.

Fifa said on Friday that they were investigating the allegations, but Neymar Sr has responded with a stunning outburst against his son's former club.

Neymar da silva Santos told Sport: They [Barcelona] are p****d off. It's all out of place. [Santos] have acted without intelligence, it's as if the owners of the club have mental diarrhoea.

"Two years have passed since my son came to Barcelona and now they're questioning a transaction made by Fifa. Who had the federative rights? Santos. And now? Barcelona. It's that simple."

In a separate case, Neymar - who scored four goals to help the Catalans down Rayo 5-2 on Saturday - has also had £31.3 million (€42.8m) worth of assets frozen by a Brazilian court following allegations he avoided paying £10.5m (€14.4m) in tax.

The ongoing legal case could also delay negotiations over a new contract for the 23-year-old - whose current deal expires in 2018 - according to his father, who added: "We, the family, are suffering from huge insecurity [to do with taxes and the legal proceedings], so that affects how we plan his career.

"We need these matters to be over. How can we extend something if we don't have tax stability? What is it that is happening? Spain has to tell me if my companies can work with Neymar Jr.

"They have to define what their position is. We are seeing various players suffering from tax sanctions.

"Why am I going to anticipate a renewal if I don't have certainty that we won't be supported in what we are working for?

"I intend to wait, stay calm and do the best for Neymar."

Manchester United were strongly linked with a move for Neymar in the summer, but the player's father reiterated his son's stand that he intends to stay at Camp Nou, regardless of interest from Old Trafford.

"They [Manchester United] phoned Barcelona and got the answer that Neymar has a contract and isn't for sale. Everyone is calm. He chose to play here and he is super happy."