Pressure has been growing on Luis Rubiales from many quartersSpain's top criminal court has opened a preliminary investigation into the country's football federation president Luis Rubiales after he kissed player Jenni Hermoso on the lips.
The prosecutors are looking into whether the incident amounts to a crime of sexual assault.
Rubiales, 46, has been widely criticised after the incident following Spain's Women's World Cup final win.
Hermoso, 33, said the kiss was not consensual.
Rubiales was suspended on Saturday by world football's governing body Fifa.
The previous day, Rubiales had insisted he would not resign.
The Prosecutor's Office says it has started the investigation because "the sexual act was not consented".
According to a statement, received by the AFP news agency from the Spanish national court, "prosecutors from the national court have opened a preliminary investigation to look into the facts, which could constitute an offence of sexual assault".
The statement indicated the court would offer Hermoso a chance to file a lawsuit.
The Spanish government has asked for Spain's Sports Tribunal (TAD) to suspend him - a request which will be discussed at a TAD meeting on Monday.
The Spanish football federation (RFEF) has also called regional federations to an "extraordinary and urgent" meeting on Monday "to evaluate the situation in which the federation finds itself".
When it announced Rubiales had been suspended on Saturday, Fifa ordered him, the RFEF and its officials and employees not to attempt to contact Hermoso, who the RFEF had threatened with legal action earlier that day.
Rubiales' mother Angeles Bejar has locked herself in the Divina Pastora church in Motril on the southern Spanish coast - the town where her son was raised - and has gone on a hunger strike because of the "inhuman hunt" against him.
She told Spanish news agency EFE the strike would continue "indefinite, day and night" - and added the "inhuman and bloody hunt that they are doing with my son is something he does not deserve".
Rubiales' cousin Vanessa Ruiz, who acts as a family spokesperson in Motril, said: "We are suffering a lot for him. He has been judged before his time.
"They (the media) don't stop harassing us. We had to leave our house. We want them to leave us alone and for Jenni to tell the truth. It's not fair."
More to follow.
