Amid strong reports Manchester United are interested in Mata, Chelsea would stand firm over their valuation for the Spain international.
As yet, there has been no formal bid from the champions but Sky Sports understands Chelsea are bracing themselves for an offer.
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.
Reports of the 25-year-old's potential departure from Stamford Bridge have gathered greater momentum this week amidst reported interest fromUnited.
David Moyes' side are seventh in the Premier League table and are in need of some fresh blood as they look to get their campaign back on track.
Tuesday's newspapers claimed the champions are set to make a move for the two-time Chelsea player of the year.
Sky Sports' Spanish football expert Guillem Balague believes a deal is likely between Chelsea and United.
"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," he said.
"Chelsea are asking for 40 million euros 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."
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."
Meanwhile, Sky Bet continue to see support for Mata to leave Chelsea before the end of the transfer window.
As of this morning the diminutive Spaniard was as short as 4/7 with online bookmaker Sky Bet to join Manchester United after starting the week as an 11/2 chance and turning the year at 25/1!
Sky Bet football trader Joe Petyt said: "We'd seen a few bets at big prices over the last month or so but on Sunday night the types of bets we were taking changed.
"We saw a few maximum bets at 11/2 and ever since customers have been taking whatever price we put up. He's now just 4/7 but that still hasn't put people off getting as much as they can on the move going through, " he added.
It would appear to finally signal a change of heart from the Chelsea hierarchy to the possibility of letting their popular player-of-the-year for the past two seasons move on.
This has led to Sky Bet opening a stay/go market and it's 8/15 that he will leave before the end of the current window and 11/8 that he stays.
One other possible option for Mata as he seeks to put himself in the frame for World Cup selection with Spain is a return to his homeland, possibly on loan. It's 20/1 that his destination is Atletico Madrid as they chase the La Liga title.