Ruud van Nistelrooy's proposed British record Stg £18.5m transfer to Manchester United was teetering on the brink of collapse last night amid farcical scenes at Old Trafford.

The signing of European football's most highly sought after striker on a five-year contract at £42,000 a week was left hanging in the balance as the press conference to signal his arrival went ahead with the Dutchman conspicuous only by his absence and his prospective new employers announcing that he had failed his medical.

Van Nistelrooy had been scheduled to arrive at 4.30 p.m. for an audience with media from around the world after having had a medical at a private hospital in Cheadle. When he failed to put in an appearance the official line was that he was on his way with the assistant manager Steve McClaren but had been held up in rush-hour traffic.

Shortly before 6 p.m. the club's finance director David Gill filed into the Europa suite with the director Maurice Watkin and their official spokesman Ken Ramsden. To a somewhat bewildered 100-strong audience Gill apologised for the delay before reading out a hastily-prepared statement.

"As you will be aware, Ruud van Nistelrooy has had a knee injury and has not been able to play for the last six to eight weeks," he said. "The key focus of our tests has been on the injured knee and we have been unable to complete all the necessary tests to our satisfaction. We will continue to conduct the tests with the co-operation of PSV Eindhoven and will communicate the position as soon as possible.

"I am pleased to announce we have concluded negotiations with both PSV and Ruud and will complete the transfer as soon as the tests have been satisfactorily concluded."

However there must be concern that the deal will not be concluded at all. Van Nistelrooy strained the medial ligaments in his right knee during a friendly against Silkeborg of Denmark on March 6th. He returned to training last week and there were no problems envisaged by either the club or the player. Indeed, the 23-year-old spoke at his press conference in Holland on Friday as though the transfer was a fait accompli.

A PSV spokesman said: "We have agreed to let Ruud stay in Manchester for another day to do more tests. If the deal is not completed on Wednesday he will have to come back to Holland for further treatment with his physiotherapists. We hope everything will be cleared up in the next 24 hours."

Asked whether the transfer was "a done deal", Gill said: "I am not prepared to say any more. Manchester United have no further comment at this time. Thank you for your patience."

At roughly the same time Van Nistelrooy was being driven away from Old Trafford, having arrived a few minutes earlier expecting to put pen to paper and seemingly oblivious to the medical diagnosis. It is believed the bad news was passed on to him in an adjoining suite.

Alex Ferguson missed the debacle which was being screened live on satellite television across the world. The United manager had flown to Spain on Monday and his chairman Martin Edwards was said to be away on club business.

When the deal was leaked last week Ferguson made no attempt to conceal his displeasure and his caution would now appear to have been justified.

To further confuse matters, a potentially acrimonious sub-plot was brewing. Edwards had stated earlier in the day that Ferguson "was obviously keen to buy Van Nistelrooy. Now he has to decide which of his other strikers he feels he can get by without".

He went on to emphasise that there would be no more transfer deals unless Ferguson recouped some of the Van Nistelrooy money by trimming a squad of 67 professionals.