Sky Sports' Spanish football expert Guillem Balague says all parties, including Mata, want the deal to happen.
The attacking midfielder - a £23.5m signing from Valencia in 2011 - has found first-team opportunities limited under Jose Mourinho this season, playing 90 minutes on just three occasions.
And Balague revealed on Revista de La Liga: "Manchester United and Chelsea are negotiating the future of Juan Mata - and the idea is that Mata, who Chelsea are happy to let go, goes to Old Trafford in this transfer window.
"Chelsea are asking for £32million or with Wayne Rooney as part of the deal. Manchester United have said no to the money and no to Rooney - but I am under the impression that a deal will be reached because it benefits everybody.
"Manchester United need quality, Mata needs to get out of the situation he is in, and it would reinforce United for their meetings with (Chelsea's title rivals) Manchester City and Arsenal, which is clever from Jose Mourinho."
Talks between the two rivals are understood to be "progressing well' which came after we learnt that Chelsea wanted in excess of £35million for the diminutive midfielder.
One man who remains unconvinced by Mata's proposed arrival at Old Trafford is former Manchester United defender Gary Neville.
"That's a lot of money, 35 million quid, but they need a signing," Neville said on Monday Night Football.
"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 him? 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?
"They would have to change to accommodate Juan Mata in the way they normally play. They normally play with wide players. Sometimes they tuck in, but generally they have wide players and the thing for me is where is he going to 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."