The Spaniard was set to arrive by helicopter on Thursday, but some late bartering by Chelsea for Mohamed Salah, plus poor flying conditions, has delayed the move
Manchester United are not concerned by the delay in signing Juan Mata from Chelsea and expect to wrap up the deal on Friday.
Mata was due to fly into Carrington by helicopter on Thursday, with the club erecting a temporary helipad within the training centre.
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United believe Chelsea's negotiations for Egypt international Mohamed Salah, effectively Mata's direct replacement, put a brake on proceedings, while poor flying conditions increasingly became a factor as the day wore on.
The Premier League champions, therefore, are confident that the £37 million (€45m) club record signing will be finalised on Friday.
Despite the delay, Mata is still expected to make his United debut against Cardiff City at Old Trafford next Tuesday.
The match against Ole Gunnar Solskjaer's side will come exactly a week after talks over Mata accelerated. Informal discussions between the two clubs were held at the beginning of this week, with United weighing up a formal bid and Chelsea prepared to sell.
The deal has moved at remarkable speed since then, with Jose Mourinho sanctioning Mata's sale to facilitate the purchase of Salah from Basel. The Spaniard edged closer to United on Wednesday after missing first-team training, and it emerged later that evening that Salah was lined up by the Blues.
Arsene Wenger complained on Thursday that the timing of the Mata transfer is unfair, given that the 25-year-old playmaker will not have to play against his former club for the Red Devils this season, but will feature against Mourinho's title rivals in Manchester City, Arsenal and Liverpool.