Jose Mourinho has admitted he shouted "son of a b****" towards Eva Carneiro but denies using the insulting phrase with sexist connotations.
Carneiro is in the midst of a legal battle against Chelsea Football Club, claiming constructive dismissal after she left Stamford Bridge in controversial circumstances last September.
She also has a separate personal case against Mourinho for alleged victimisation and discrimination.
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The case got underway at Croydon Employment Tribunal in south London on Monday and is expected to last anywhere between seven and ten days. However, a decision can be made at any time.
Mourinho was not present but the tribunal panel read a statement written by the Portuguese in which he admits using the term "filho da puta", meaning "son of a b**** or whore", but also claimed it was a saying he used often.
He wrote: "Filho da puta is a phrase I often use, all of the players know it. There is no sexist connotation in the use of the phrase - it is just like saying 'f*** off'. In the world of football, a lot of swear words are used."
It was also claimed by Mourinho, who left Chelsea in December and is now manager of Manchester United, that Cesc Fabregas had been using the Spanish equivalent of the term, suggesting it was common for people in football to curse in their native tongue.
Mourinho said: "Cesc and I both speak English well, but in the heat of the game we both swear in our mother language.
"Eva was not on the pitch at that point in time."
It is believed Chelsea have already offered Carneiro £1.2m to settle outside of a tribunal but this was rejected by the experienced doctor. An agreement between all three parties is needed to avoid a tribunal.
An argument submitted to the panel read: "The respondents have taken these steps only because they believe that it is in no-one's interests that this dispute should be determined through litigation.
"They are conscious that, whatever the facts of the matter, it is likely to be widely and incorrectly assumed that they could have avoided this coming tribunal."
Carneiro was believed to have been forced out of Chelsea after Mourinho criticised her and physio Jon Fearn for entering the field of play to treat Eden Hazard during a game against Swansea City.
Mourinho later described them as "impulsive and naive" and stopped Carneiro from sitting on the first-team bench during matches. While Fearn is still employed by the Blues, Carneiro parted company weeks after the incident.
An investigation by the Football Association cleared Mourinho of using discriminatory language towards Carneiro but independent board member Dame Heather Rabbatts later criticised them for not interview the 42-year-old doctor.