The row over Gabriel Heinze's proposed move to Liverpool is threatening to spill over into open warfare after Sir Alex Ferguson confirmed Manchester United are investigating the possibility their north-west rivals made an illegal approach for the Argentina defender.

United have flatly refused to do business with Liverpool, even though Rafael Benitez has matched United's £6.8million asking price for the 29-year-old.

Although Heinze's agent claims to be in receipt of a letter which effectively gives the full-back permission to leave Old Trafford, United chief executive David Gill does not believe it over-rides the player's contract, which still has two years to run.

In any case, Gill insists he verbally informed Heinze's agent that United would not be prepared to do business with any of their main Premier League rivals, specifically Liverpool, Arsenal and Chelsea.

Currently on a short break following his participation at the Copa America, Heinze is said to be considering a legal challenge to Gill's view.

Yet the United stance only backs up Ferguson's previously stated opinion that Heinze had no chance of joining the Champions League finalists, a position that has only hardened over the past few days, with the United boss adding a further twist to the saga.

"Gabriel Heinze will not be joining Liverpool," he said immediately after his side's 6-0 pre-season win over Chinese League outfit Shenzhen in Macau.

"We are examining some of the statements coming from his agent and when contact was first made with Liverpool.

"We are not happy with the agent's conduct in the matter and we are examining that as well, but it will take a couple of days before we have anything more to say."

By coincidence Liverpool are only 40 miles away from United, having landed in Hong Kong yesterday ahead of the bi-annual Premier League Asia Cup competition.

Speaking before Ferguson dropped his bombshell, Benitez confirmed he was keen for Heinze to become the first player to head down the East Lancs Road from United to Liverpool since Phil Chisnall in 1964.

"We made the offer and they rejected it. Now the lawyers are working on it," said the Reds boss.

"We have to wait. We are still trying to push the deal through because he is a good player and a player we like."

It means United are heading towards the start of the defence of their Premier League title with two transfer wrangles needing to be sorted out.

Ferguson is still hopeful of having Carlos Tevez on board for the season's opening game against Reading on August 12.

However, the Red Devils chief already knows he will be without influential midfielder Paul Scholes.

The former England star flew home to Manchester earlier in the day after scans on his knee revealed "a slight discolourment" according to Ferguson.

"Paul felt his knee in the last game, so we sent him for a scan which showed some discolourment around the cartilage," he said.

"We have sent him hope for a 'scope' to see what the damage is.

"I do not think it is particularly serious but it is enough for us to send him home to make sure he is going to be okay and we expect him to be out for around three weeks to a month."

A month's absence would be enough for Scholes to sit out not only the Reading encounter but the trip to Portsmouth three days later and the following weekend's Manchester derby at Eastlands.

With Owen Hargreaves yet to feature in United's pre-season campaign due to a knee injury, Ferguson is facing the prospect of being without two senior midfield men for the new campaign.

At least he was finally able to introduce £17million teenager Nani for his debut, a fitting move given the third game of United's Far East tour was taking place in a former Portuguese colony.

The former Sporting Lisbon winger showed sporadic glimpses of his talent on a hot and humid evening, firing home a fine third goal for United before the break before galloping downfield on one excellent burst to help set up fellow countryman Cristiano Ronaldo for a well-received fifth.

"Nani has not done a great deal of training but that was a good start for him," said Ferguson.

Man of the match Ryan Giggs was also on the scoresheet, as were Wayne Rooney, John O'Shea and Chris Eagles on what amounted to little more than a stroll for the visitors.