Chelsea’s former team doctor heard José Mourinho call her a “daughter of a whore” in Portuguese when she ran on to the pitch during a Premier League match to treat an injured player last year, an employment tribunal has been told.

Dr Eva Carneiro, 42, is claiming unfair dismissal against Chelsea, and sex discrimination and harassment against the club’s former manager following the incident at the game against Swansea last August.

On the opening day of what looks set to be a bruising two-week trial, lawyers for Chelsea revealed that Carneiro was offered £1.2m to settle her claims, but instead decided to take the case to an open hearing, in which private texts and emails among the Chelsea hierarchy are expected to be exposed and Mourinho, now manager of Manchester United, will face cross-examination.

In a skeleton argument, they told the tribunal the cash offer was far more than “she could realistically recover even if she succeeded on all her claims”. They said she is now making an “extravagant compensation claim”.

Carneiro’s decision to run on to the Stamford Bridge pitch to treat Eden Hazard meant the team was temporarily reduced to nine men, and Mourinho afterwards called her and the physiotherapist Jon Fearn, who went on with her, “impulsive and naive”. She did not appear on the bench again for first-team duties and later left the club.

“This is a tale of two employees: one good, one bad,” Carneiro’s lawyers said in their opening argument. “The bad employee forces the good employee out of the job of her dreams and the employer does nothing to stop it. The bad employee berates, sexually harasses and demotes the good employee for carrying out her professional duties.” Chelsea and Mourinho deny the claims.

Lawyers for both sides made clear a key part of the case would hinge on the precise meaning of Portuguese swearing. The Oxford University professor Simao Valente, described as an expert in Portuguese swearing, will give evidence. Mourinho is also expected to take the stand, as will the Chelsea chairman, Bruce Buck, and club director Marina Granovskaia, one of Roman Abramovich’s most trusted advisers.

The three-person tribunal heard that Mourinho called Carneiro “filha da puta” as she went on to the pitch to treat Hazard in the match against Swansea. Mourinho, in his witness statement denies that and claims he shouted “filho da puta”, which means son of a whore, and that it was not directed at the doctor.

“As she ran on to the pitch she heard clearly from behind her the words filha da puta,” said Mary O’Rourke QC, appearing for the claimant. “She’s a Portuguese speaker. It was not filho da puta, it was filha da puta … you say filha da puta when you are denigrating a woman. He is saying it to the back of the claimant who is doing something he didn’t like … that is the context.”

Mourinho in his former role as Chelsea manager. Photograph: John Walton/PA

Daniel Stilitz QC, appearing for Chelsea, said Mourinho’s evidence was that he shouted filho da puta.

“Filho da puta is a phrase he often uses,” he said, adding that it meant son of a bitch. “There is no sexist connotation.”

He said that Mourinho used the phrase frequently at Chelsea’s training ground and during matches.

Carneiro claims that Mourinho also abused her for going on the pitch to treat a head injury in a game against Fiorentina days previously. Her lawyers allege Mourinho shouted at her: “Now we’re going to shit ourselves. Every time someone goes down with a head injury we’re going to shit ourselves.”

She also claims: Chelsea failed to act to stop sexist chanting directed towards her at away games at Manchester United and West Ham; there was a lack of female changing facilities; there was a failure to provide her with a club suit; and there were “regular sexually explicit comments from colleagues”.

After Mourinho allegedly abused her in the Swansea game, he told the club’s head of communications, Steve Atkins, that he didn’t want Carneiro on the bench. Her lawyers claim that he said “she works in academy team or ladys [sic] team not with me”.

Carneiro’s lawyers also said Granovskaia texted Carneiro on the evening of the Swansea match saying: “people who know, know you did nothing wrong. People who know José also know he is ranting.” She added: “I don’t think there’s a salary that allows public attack.”

In the following weeks, Bruce Buck, Chelsea’s chairman, told Carneiro that she would not be involved in the first team. Caneiro replied that she had acted in compliance with the rules of the game and her duties as a doctor, but he told her she would only return to work “in an adjusted role” so she resigned.

Chelsea and Mourinho will argue that Carneiro would still be in her job if she had not resigned and said that she had been “provocative” and “refused to engage in steps to rebuild her relationship with Mourinho”.

“The claimant’s suggestion that Mr Mourinho’s language was gendered and targeted specifically at her is plainly unwarranted in the light of the footage,” their lawyers said. “Indeed she did not allege that the language used was discriminatory until well after the event. Mr Mourinho’s language was, again, far from unusual in the context.”

They also allege that in talks with Granovskaia, Carneiro said she was willing to “draw a line under what happened” in exchange for demands including a 40% pay rise to £400,000, a bonus scheme, an immediate return to the bench and a “substantial payment” in compensation for distress.

They allege Carneiro’s attitude to work more broadly had raised concerns. They said she was “increasingly pre-occupied with developing her profile”, including signing autographs, posing for photos and nominating a first-team player when she did an ice bucket challenge. They said she tried to sit behind Mourinho in televised matches and “secretly briefed against Chelsea to the media”.

After the incident against Swansea, they state that Granovskaia warned Carneiro not to go on social media, but she did so, thanking the public “for their overwhelming support” on Facebook. Buck was shocked by this and saw it as “changing the whole dynamic of the situation” and Mourinho was “very unhappy”.

Mourinho was in charge at Chelsea until his sacking last December following a run of poor form for the team and has since taken over at Manchester United. He is expected to give evidence on Monday.

Mourinho was cleared of using discriminatory language towards Carneiro following an investigation by the Football Association.

Afterwards, Carneiro and the FA’s independent board member, Dame Heather Rabbatts, criticised the governing body for not interviewing the doctor as part of its investigation.

Carneiro has also had backing from Fifa’s medical chairman, Michel D’Hooghe, who contacted the doctor to offer his support and that of the world governing body. He has backed Carneiro’s insistence that she was simply doing her job.

The hearing continues.