Previously cordial boardroom relations between England's two most successful clubs have deteriorated over Heinze's future. The player is keen to join Liverpool but United's manager, Sir Alex Ferguson, has insisted he will not sell to his arch-rivals, who are expected to be strong contenders for the Premier League title which his squad won last season.
United gave permission to Heinze's representatives, the Buenos Aires-based company Soccer SA, to seek a new club for the player this summer on the proviso that a £6.8m fee was secured but David Gill, the Old Trafford chief executive, has insisted that depended on the 29-year-old not joining a rival for domestic honours.
Liverpool and Heinze are preparing to contest that, claiming a valuation letter from United does not mention any such restriction and that the defender should be allowed to join them because they met the asking price last week.
"We made an offer which they rejected. The lawyers are now working on it and so we have to wait," Liverpool's manager, Rafael Benítez said yesterday. "It's clear he's a player we like and he's a very good player. That's the reason why they don't want him to leave for us."
Ferguson responded by announcing United's intention to probe the actions of Heinze's representatives. He is furious at what he perceives to be moves by the player's agents to force through a transfer to Liverpool.
"We are examining some of the statements coming from his agent of when the contact was first made, but at the moment we have nothing more to say," Ferguson said after his team had beaten FC Shenzhen 6-0 in Macau. "We are not happy with the agent's conduct in the matter and we're examining that.
"There hasn't been any change in our stance because Heinze is not going to Liverpool as far as I am concerned."
The Madrid-based agent Roberto Rodríguez and Heinze's brother, Sebástian, have acted as advisers to the player, who is on a summer break after his involvement with Argentina in the Copa América, and Ferguson last week revealed suspicions that Heinze's future was being driven by a third party. "Heinze's agents are rolling the ball all the time but no matter what the agent thinks, we are in the driving seat," he said.
Gill has dismissed suggestions that Heinze may invoke a Fifa ruling which would allow him to buy out the remaining two years of his contract and says a signed letter allowing a transfer for a set fee is now meaningless, despite the insistence of Liverpool and the player's representatives that the agreement is binding.
Benítez believes Heinze's case is strong enough to undermine United's stance and will wait for as long as the player fights on, with a court hearing looking an increasing possibility. Heinze has made it clear he is keen to link up with his compatriot Javier Mascherano at Anfield and is ready to battle for the move even though his actions risk antagonising United supporters.
While the Heinze row rumbles on, Liverpool's captain, Steven Gerrard, has turned his attention to the season ahead. Benítez's squad face South China today in the first game of a tour to Asia, and Gerrard says winning the Premier League is more important than lifting the European Cup.
Gerrard, who captained Liverpool to Champions League success in 2005, is excited at the arrivals of Fernando Torres, Ryan Babel, Yossi Benayoun and Andriy Voronin, and believes the club have the ability to mount a serious challenge for the league title, which they last won in 1990.
"We're very ambitious and we know what's expected from us," he said. "The manager has been backed with good money this summer and he's spent it well but now is the time for us to deliver. The Premier League is our main priority; that's the one we want most of all. If I could pick one trophy to win it would be the league because from a purely selfish point of view it's the only one I haven't won. Having said that, if we win the European Cup this year you won't see me upset."
Steve Finnan has agreed a new three-year contract at Anfield and is expected to sign when the team return from Asia.