Manchester United have launched an investigation into Liverpool's conduct over Gabriel Heinze's protracted move away from Old Trafford, manager Alex Ferguson said on Friday.

"We are investigating Liverpool's role in this. We are not letting them off with this," Ferguson told reporters.

Heinze was wanted by Liverpool until a Premier League arbitration panel upheld United's claim that the Argentina international was not permitted to move to one of their major domestic rivals.

Defender Heinze instead sealed a transfer to Real Madrid this week but United are not prepared to let the matter rest.

Asked whether he felt Heinze had been the subject of an illegal approach, or been `tapped up' by Liverpool, Ferguson added: "We'll see how it comes out. (Chief executive) David (Gill) is working on it at the moment and he will get to the bottom of it."

Liverpool manager Rafael Benitez had expressed his anger that Heinze had not been permitted to move to Anfield, claiming that the tribunal had wrongly sided with United when making their decision.

Ferguson responded: "I'm disappointed about the stuff he has come out with. He has a wee bit of a chip on his shoulder about it all."

Heinze's departure from United after a three-year spell followed a dispute over a letter from the club giving the 29-year-old defender the right to leave for an agreed fee.

Ferguson said he was "disappointed" at how the saga had unfolded and questioned the role of Heinze's agent Roberto Rodriguez in the saga.

"I have no axe to grind with Gabi," Ferguson said. "When he played he was a warrior and a committed player but the issue is how much he really listened to us rather than his agent.

"We are disappointed. I don't think Gabi was getting the right information from his agents during the negotiations we had with him, and that's a disappointing feature."