Manager David Moyes, whose team are currently seventh in the Premier League table, previously insisted that United remain capable of attracting the best players in the world despite their current struggles, and rumours suggest that he will bid a club-record fee to try to sign Mata.
"That's a lot of money, 37 million quid, but they need a signing," Neville told Sky Sports News. "Does he fit with what I would call the typical philosophy of Manchester United? I would say no.
"The first question, I think, is where are you going to play? Wayne Rooney and Robin van Persie are up top if they are fit so where are you going to play him? Are you going to play him off the left or off the right? We've seen Kagawa play off the left, we saw Kleberson play at times off the left, we've seen Veron at Manchester United move to the left because you can't play central midfield. Maybe they have to change the philosophy and maybe that's what David Moyes is thinking. Maybe he wants to play narrow wide players and maybe a three in midfield.
"They would have to change to accommodate Juan Mata in the way they normally play. He's obviously a fantastic football player, there's no doubt about that, but one thing it does do, I suppose, is that David Moyes, Manchester United and Ed Woodward need to sign a big player. They need to make a noise and if they get him in it will attract potentially other players - and they need three or four players. What it could be is the start of something to lead to other things, but typically I wouldn't say he fits."
United host Sunderland in the second leg of their Capital One Cup semi-final on Wednesday.