Jose Mourinho last night revealed that he confronted Adrian Mutu over suspicions the player was using cocaine just days after joining Chelsea.

The Romania international striker was yesterday dismissed from the job for gross misconduct after it emerged he faced an English Football Association hearing next week for a failed drugs test. That prompted the Professional Footballers' Association (PFA) to claim that Chelsea had failed in their "duty of care" to an employee who has had "serious personal problems".

Mourinho said he recognised problems immediately. "When I met him on his first day in the pre-season in July, and he was with his two agents Mr (Victor) Becali and Gica Popescu, I told all three 'I have information that you are on cocaine'," he said.

"All three were laughing, denying, saying this was a lot of lies about Adrian. After that I did not speak with them again because they denied the situation.

"For a long period we saw now and again strange behaviour. Arriving late a few times, not coming in to train other times. A doctor visiting his house and the apparent reason was just headaches. Injured when nobody knows how it happened - for example he was on the bench and did not play against Paris (Saint-Germain), yet the next day he was injured.

"We began to question, and the club doctor, because he has some experience that we do not have, was analysing with different eyes and he arrived at the decision that maybe, yes. I would never sign him again. Not just because of the drug, but because he called me a liar."

It was the first verbal attack from Chelsea as the battle lines were being drawn in what is likely to become a costly legal process. The club have engaged Jonathan Taylor, head of Hammonds' sports law group, with the FA appointing as prosecuting counsel Mark Gay, a board member of the British Association for Sport and Law.

As well as representation from the PFA, it is understood Mutu's advisers were last night in advanced negotiations with Nick Bitel to act as defence counsel. The Culture, Media and Sport select committee called Bitel as an expert witness in its formulation of a drugs in sport report, and his testimony supported the FA's allowance in its rules for a divergence in the considerations of recreational and performance-enhancing drugs.

This, along with Mutu's willingness to undergo a programme of rehabilitation, is expected to form the basis of Mutu's defence.

The question of liability is central to the legal dispute. Following next week's FA hearing Chelsea may seek recourse to claim compensation from Mutu or any club that recruits him, since the dismissal writes off a £12 million asset from their books. Mutu would be entitled to the defence that it also conveniently saves Chelsea around £11 million in his wages, and it is one the PFA is already citing.

"They're trying to look for compensation and saying he can't play anywhere else," said the PFA chairman Gordon Taylor, though Chelsea merely indicate they "reserve the right" to do so and no decision has yet been taken.

"If (his contract) has been terminated wrongly, then there could be compensation for the individual," Taylor said.

Mourinho's testimony that he was aware of Mutu's drug abuse four months ago challenges the belief that the problem is "one off" and it was that which prompted Chelsea to target test the player.

Taylor confirmed Mutu's mind is troubled by the developments, since Chelsea's actions have "confirmed his worst fears". Considering the circumstances of Mark Bosnich, who has not returned to the game almost two years after becoming the last player to be dismissed by Chelsea for cocaine use, Mutu's career is in tatters.