The rivalry between Chelsea and Manchester United as they battle for three trophies has intensified after an extraordinary war of words between José Mourinho and Cristiano Ronaldo.

The Chelsea manager is usually full of praise for a player he attempted to sign two years ago, but yesterday he launched a devastating attack on his fellow Portuguese, questioning his attitude and maturity and effectively branding him a liar. Jorge Mendes, the agent who represents both superstars, will not have known which way to turn.

Mourinho was replying in typically forthright fashion to Ronaldo’s criticisms of his complaint that referees do not award penalties against United. Ronaldo said that Mourinho was an attention seeker who refuses to admit his mistakes, though he may have regretted being so outspoken given the ferocity of the response.

“A player that wants to be the best in the world needs to behave well, to keep quiet and to have sufficient honesty and maturity to verify that against the facts that I have shown,” Mourinho said. “If he says that it is false that Manchester United have conceded penalties that were not given, it’s lies. And if he is a liar he will never reach the highest level that he desires in football.” The tension between the clubs was further inflamed when Carlos Queiroz, another Portuguese, opted to speak out on Ronaldo’s behalf and criticised Mourinho’s lack of humility. “Mourinho has his own style, he always tries to divert everyone’s attention to the points which are convenient for him,” the United assistant manager said.

“However, we are different because when we can’t win we at least have the humility to recognise the others’ merits and we learn from our opponents’ strengths.”

“The whole world knows how Mourinho is,” Ronaldo had said. “He always has to say something to gain attention, especially when he is not happy with his players. He never recognises when he is wrong.”

Mourinho’s outburst is the latest in a series in recent weeks as the burden of attempting to win the quadruple and retain his job begins to take its toll, with United, Rafael BenÍtez, the Liverpool manager, and referees having come under attack.

Chelsea will continue their attempt to claw back United’s three-point advantage at the top of the Barclays Premiership against Bolton Wanderers at Stamford Bridge tomorrow amid concerns that their title rivals could have another advantage.

Sir Alex Ferguson’s side face Everton at Goodison Park in the knowledge that their opponents stand to benefit financially if United win the league as they will receive £500,000 from Old Trafford in another instalment of Wayne Rooney’s transfer fee.

Chelsea have not registered any dissatisfaction, with the FA Premier League insisting that there is no conflict of interest. Everton can recover the potential loss by finishing just one place higher in the Premiership and have the further incentive of fighting for Uefa Cup qualification.