Heinze, who finally severed his ties with United on Wednesday by completing a surprise move to Real Madrid, had challenged United's refusal to sell him to Liverpool at a Premier League arbitration panel, which ultimately ruled against the 29-year-old earlier this week.

While admitting that they had given Heinze permission to seek a transfer to a club willing to pay a £6.8 million asking price, United insisted they also verbally warned the player that he would not be allowed to move to a domestic rival.

Liverpool contested that stance by matching United's valuation last month, an offer which was swiftly rejected by the Premier League champions, whose case for denying Heinze a move to Anfield was supported by the Premier League.

Now United are determined to examine the part played by Liverpool throughout the two-month saga. When asked whether United were accusing Liverpool of making an illegal approach, Ferguson said: "We're investigating at the moment. David [Gill, United's chief executive] is working on that at the moment and he'll get to the bottom of it.

"They had no chance of winning that case. He [Benitez] obviously didn't study the Premier League rules, but I'm disappointed with some of the stuff he's come out with. He's got a chip on his shoulder about it. I've no axe to grind with Gabby. But the issue is without question how much he really has listened to us rather than his agent."

Liverpool refused to respond to Ferguson's comments. The United manager, who also dismissed claims by Benitez that United were allowed to sign Carlos Tevez from West Ham much quicker than Liverpool were able to secure the services of Javier Mascherano last January, expects Louis Saha to be fit to take a place on the substitutes' bench for the Premier League game with Tottenham at Old Trafford tomorrow.

With United searching for their first win of the season and Spurs manager Martin Jol under pressure, both sides are hoping to avert a crisis.