Mata became United's record signing back in January after a £37.1 million transfer from Chelsea, per BBC Sport. But speculation has emerged as to whether new boss Louis van Gaal will be able to accommodate the 26-year-old in his United XI and that Barcelona are lining up a bid for the playmaker, per Anthony Chapman of the Daily Express.
But De Gea, Mata's teammate with both Spain and the Red Devils, has called on the club to keep hold of a player he feels has a massive role to play at Old Trafford, per Movistar (h/t Sky Sports):
"I would not sell Juan Mata. He is a very important player for us. We have taken a qualitative leap with him and he has adapted very well."
The former Chelsea man was offloaded by Jose Mourinho in January, with Mata's qualities not compatible with what the Portuguese boss demands from his players. In truth—and somewhat unfortunately for Mata—Van Gaal is of a very similar mindset to his former Chelsea manager.
Nonetheless, Mata has stated he is looking forward to working with Van Gaal, as noted here by Old Trafford News:
The Dutchman's teams have always played with power and a purpose. Mata has many desirable attributes, but unfortunately for him, physicality is not one. He is a player wonderfully adept at finding space, technically superb and unyieldingly creative. But it's not in his make-up to track back or put tackles in.
Under David Moyes, Mata was regularly played in a wide role, typically floating in off the right-hand side. But that's by no means his best position, and it's certainly not where he'll play under Van Gaal, who demands industry and energy on the flanks.
The major questions are whether or not Mata can oust Wayne Rooney from the No. 10 berth, or whether United will even line up with someone off the centre-forward. Van Gaal has utilised a host of formations in the past, but his go-to style is 4-3-3, a system that is admittedly difficult to see Mata—neither an orthodox midfielder nor a genuine wide player—flourishing in.
Van Gaal will most likely rid this United squad of plenty of dead wood—a category in which Mata certainly does not belong—and look to stamp his mark on United immediately. He is a very proud man who stands staunchly by his principles, and whilst he will surely give the Spaniard a chance to prove himself, if he isn't a stylistic match, don't expect any liberties from the Dutchman.
If you're looking for a creative No. 10 who can score and make goals, then there aren't many better than Mata around. He is a player who is talented enough to build a team round, and he's shown in his time at Chelsea that when you do so, he's a genuine world-class talent.
But managers like Van Gaal and Mourinho are stubborn. They have a way of playing, and they'll stick to it, regardless of the players they might have at their immediate disposal. If Van Gaal doesn't feel as though Mata is the right fit, he could be on his way out.