Prosecutors at Spain's top criminal court said Monday they had opened a preliminary investigation into Spanish football chief Luis Rubiales' forcible kiss on the lips of World Cup player Jenni Hermoso on grounds it could constitute a crime of "sexual assault".

"Prosecutors from the National Court have opened a preliminary investigation to look into the facts, which could constitute an offence of sexual assault," a court statement said.

They would also contact Hermoso to offer her a chance to file a suit within 15 days, the statement said.

The president of the Spanish football federation (RFEF), provisionally suspended from his post by FIFA on Saturday, could face an extended sanction if the country's sports court accept complaints against him in a meeting on Monday.

After Spain won the Women's World Cup in Sydney on August 20, Rubiales sparked a massive backlash after forcibly kissing Hermoso on the lips during the medal ceremony.

Hermoso later said the unwanted kiss had left her feeling "vulnerable and like the victim of an assault", with a statement on social media describing it as "an impulsive, macho act, out of place and with no type of consent on my part".

The National Court said it was opening the investigation in light of the "unequivocal nature" of her statements, saying it was necessary "to determine their legal significance".

"Given the public statements made by Jennifer Hermoso, the sexual act she was subjected to by (Luis) Rubiales was not consensual," the court statement said.

Legal experts would also contact the player "to offer her the option of legal action, giving her the chance to contact National Court prosecutors within 15 days for information about her rights as a victim of an alleged sexual assault... should she wish to file a complaint", it said.

"In order to proceed with a case for sexual assault, harassment or sexual abuse, it will be necessary for the injured party or their legal representative to file suit, or the public prosecutors' office."

If Hermoso decides not to file suit, it will make it "difficult" for prosecutors to press ahead with the case, legal sources told AFP.

So far, the court said it had received six complaints about Rubiales' kiss, which without consent constitutes an offence of sexual assault under Spain's recently-updated criminal code.

None were filed by Hermoso.

World football governing body FIFA provisionally suspended Rubiales for 90 days but the 46-year-old could face a longer suspension from the Spanish government, if the sports court opens proceedings against Rubiales for "very serious" offences or an "abuse of authority".

Spain's top sports court (TAD) was meeting online.

The Spanish government has said it will take action against Rubiales if the sports court gives them the go-ahead.

Some 81 players went on strike from the women's side in protest after the federation chief refused to quit, while 11 members of RFEF women's football staff offered to resign -- controversial coach Jorge Vilda did not.

- Hunger strike -

With Rubiales still under fire, his mother Angeles Bejar on Monday locked herself in a church in the southern seaside town of Motril, where the RFEF chief was raised, and went on hunger strike in protest against the treatment of her son.

"There is a harassment that is not fair. His mother who has a deep faith, has found refuge in God, she has gone on hunger strike, she does not want to leave the church," said Vanessa Ruiz Bejar, Rubiales' cousin.

"We want Jenni to tell the truth because she has changed her statement three times. His family is suffering greatly."

But the criticism of Rubiales continues.

Andres Iniesta, who scored the only goal in the 2010 men's World Cup final to give Spain the trophy for the first time, said Rubiales' conduct had "tarnished" the women's achievement.

"It's a shame that a beautiful story that so many players have built over so many years has been soiled," he said on social media.

Politician Yolanda Diaz, Spain's Second Deputy Prime Minister, also criticised those who applauded Rubiales on Friday as he refused to resign and railed against "false feminism".

They included the coach of the men's national team, Luis de la Fuente, and women's coach Vilda, who have both since condemned him.

"The coaches who applauded Mr. Rubiales are not are not fit to continue in their posts," she said Monday.