Furious Manchester United boss Sir Alex Ferguson has vowed the Old Trafford outfit will not let Liverpool 'get off' with any dishonourable conduct in the Gabriel Heinze affair.

Ferguson has revealed United chief executive David Gill is currently investigating what contact Liverpool had with Heinze over a proposed move to Anfield, which fell through this week, triggering the defender's eventual transfer to Real Madrid.

Although Ferguson did not use the words 'tapping up' when he was asked whether United felt that is what had happened, he replied: ''We will see.''

Chief among United's concerns is how solicitor Richard Green, who advises Liverpool on much of their legal work, came to be acting for Heinze in his attempt to prove a letter - signed by Gill and stating a fee which would be acceptable for the player - was an agreement to sell.

A three-man Premier League tribunal rejected the claim on Tuesday but, with Liverpool supposedly having no direct involvement in the case, United want to know how Heinze secured Green's services, given the 29-year-old still had two years of his Red Devils contract to run.

United's unhappiness with Liverpool has only increased following Rafael Benitez's outburst in which the Reds coach, while stressing his amazement at the Premier League's ruling, effectively claimed the Red Devils enjoyed preferential treatment, not just over Heinze but also in the drafting of fixtures and the 'smooth' move of Carlos Tevez from West Ham compared with the deal which saw Javier Mascherano join Liverpool in January.

It was rant which smacked of sour grapes and could yet land Benitez in hot water with the Premier League.

''What Rafa said is a bit churlish,'' declared Ferguson.

''He obviously did not study the Premier League rules because he had no chance of winning the case.

''But we are looking at Liverpool's whole role in this.

''David Gill is working on it at the moment. We will get to the bottom of it and see what comes out because we are not letting them off with it.

''I am really disappointed with Rafa. He is going on about Saturday fixtures after European games. Well, he wants to look at our fixture list over the last two or three years. Maybe then he would have something to complain about.

''As for Carlos Tevez, it took about three months.''

Ferguson does not believe Heinze was responsible for the rumpus and is hugely critical of the player's agent, Roberto Rodriguez, who, he claimed, will benefit financially from the player ending his three-year association with United.

''I don't think Gaby was getting the right information from the agents in terms of our negotiations with him, which is a disappointing feature," he said.