Naybet, 28, is rated one of the best and toughest defenders in Spain, where he plays for Deportivo La Coruna and is known as "El Loco". His former clubs include Nantes and Sporting Lisbon. Real Madrid have tried to sign him on two occasions, while last week Liverpool were reported to be interested. Sir Alex Ferguson sought his signature after looking round Europe for a new defender when long-term injuries ruled out Ronny Johnsen and Wes Brown.
Naybet will be registered in time to play in Europe, but he must apply for a work permit and that could make him unavailable for a few weeks.
Ferguson is relieved to have signed a leading defender after moves for others - including the veteran Jurgen Kohler - collapsed. That Naybet may be kept on the sidelines for a couple of domestic games while his permit is processed will not be a problem for United.
The deal takes Ferguson's spending to pounds 10m, including the Italian goalkeeper Massimo Taibi, who is joining from Venezia. United are paying more for Naybet than they wanted, but there is interest from other quarters and Ferguson is under pressure to find a quality player quickly.
The transfer activity comes after a summer when United did not spend and following the manager's request for funds that was heeded by the plc board. United could recoup some of the money by swapping their Dutch midfielder, Jordi Cruyff, to Deportivo later in the season. A swap was discussed but the Spanish transfer window has now past and business will go on hold until a later stage of the campaign.
The Sheffield Wednesday manager, Danny Wilson, and chairman, Dave Richards, will meet today in an effort to resolve the Benito Carbone affair. Carbone is currently in Italy, having stormed out of The Dell on Saturday after being told he was among the substitutes for their match with Southampton.
However, Wilson has spoken to the striker since then and is expecting him to return to England this weekend.
Wilson said: "I will speak to the chairman tomorrow and we will discuss the future [for Carbone] then."
Carbone, who is on the transfer list at Hillsborough, has been fined two weeks' wages after his vanishing act, according to the club's official Website. The 28-year-old headed back to his native country while his team-mates were being beaten 2-0 by Southampton to remain bottom of the Premiership.
Liverpool's Norwegian international defender, Bjorn-Tore Kvarme, has signed a two-year contract with the French first division side St-Etienne. Kvarme, 27, who has six caps for his country, was transferred for a fee estimated at around Fr10m (pounds 960,000).
The former Rosenborg Trondheim defender became the 11th player to leave Liverpool since the French manager, Gerard Houllier, took sole charge at Anfield in November.
Roy Keane, the Manchester United captain who missed yesterday's Premiership meeting with Newcastle United, should be fit for the Republic of Ireland's European Championships qualifier against Yugoslavia tomorrow despite a minor knee injury.
The Republic's coach, Mick McCarthy, said yesterday: "We'll have to wait and see. He took a bang on the knee in Monaco but he'll be fine. He'll be fit."