The Spaniard was set to arrive by helicopter on Thursday, but some late bartering by Chelsea for Mohamed Salah, plus poor flying conditions, delayed the transfer.
|MATA TO MAN UNITED
HOW GOAL COVERED THE STORY
|CHELSEA OPEN TO MATA EXIT
|MATA ON VERGE OF UNITED SWITCH
|CHELSEA TARGET SALAH
|MATA FLIES IN TO COMPLETE DEAL
|WENGER: MATA MOVE IS UNFAIR
As on Thursday, when Mata was originally expected to fly in to seal the switch, key personnel including doctors, a legal team and executive vice-chairman Ed Woodward, were all in place when the 25-year-old arrived.
A makeshift helipad welcomed Mata's helicopter with a team of security guards on patrol around the perimeter of the training ground.
The World Cup and European Championship winner with Spain was forced to delay his arrival to Manchester due to poor weather conditions as well as the fact that Chelsea's negotiations for Egypt international Mohamed Salah, effectively Mata's direct replacement, put a brake on proceedings.
Despite the delay, though, 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.
Mourinho, however, brushed off that criticism: "Wenger complaining is normal because he always does. It's something we know."