But, if there is a shred of truth to these rumours, United should pull out all the stops to bring Mata to Manchester and send Rooney on his way.
Chelsea confirmed that they made a bid for the unsettled striker on Tuesday.
However, the Blues have been quick to distance themselves from speculation surrounding the departure of Mata and David Luiz, whose name has also been linked with a swap for Rooney.
In a statement published on the club’s official website, Chelsea said: "A written offer to Manchester United for the transfer of the striker had been made but that no other players are part of the offer."
United, who are thought to be reluctant to sell Rooney to one of their direct Premier League title rivals, rejected the advance, according to the BBC.
There have been rumblings about Rooney’s future for some time. Yet, until now, the forward has been publicly quiet about his feelings.
Moyes, who is on a preseason tour of Australia and the Far East, told members of the assembled press in Bangkok (as reported in the Guardian):
Overall my thought on Wayne is, if for any reason we had an injury to Robin van Persie, we'll need him. It's going to be a time to see how I work with Wayne. Maybe in a year's time we might have to look at something else. The first year, I have to get a chance to see the players and how best to use them. I've got to ensure it's not just him and we don't concentrate on him. Manchester United isn't about Wayne; Manchester United is about the team, the club.
This was either a disastrous PR move on Moyes’ part or a very well-constructed ploy to usher Rooney closer to the Old Trafford exit door.
Either way, Rooney has broken his silence and, after flying home from the preseason tour with a hamstring injury, is "confused and angry," according to a source quoted by Ian Herbert in the Independent.
United chief executive Ed Woodward has also said that there are no plans to offer Rooney a new deal beyond the remaining two years of his contract, as reported by Chris Bascombe in the Telegraph.
It now looks likely that Rooney will not be pulling on the red shirt of United next season and perhaps, if Chelsea come back with an improved deal, we may see Mata moving to the northwest.
From a United standpoint, it would be an excellent signing. Not only would the club be ridding themselves of a want-away and potentially divisive figure, they would be acquiring one of the best creative midfielders in today’s game.
Mata has made 118 appearances to date for Chelsea, where he has scored 31 goals and made 55 assists in all competitions.
Mata was the Premier League’s top assist-maker last season, with 12 assists—two more than Rooney.
The Spaniard also scored 12 goals, equaling Rooney’s tally. This made Mata one of only four players to reach double figures in both goals and assists all season.
He is a World Cup and European Championship winner with Spain and, at Chelsea, has added the FA Cup, Europa League and Champions League to his haul of honours.
The 25-year-old is a great passer of the ball and is a threat from set-pieces. He has pace, trickery and is a constant goalscoring threat. Versatile, Mata would slot in perfectly alongside Michael Carrick in midfield if Moyes opted for a 4-4-2 formation.
In a 4-2-3-1 set-up, he could also play behind the striker. Mata playing behind van Persie would pose a formidable threat to Premier League defences.
Mata is also a likable character and would be more likely to keep dressing room harmony in what will be a season of huge transition both on the pitch and behind the scenes at Old Trafford.
A Chelsea switch could also be the right move for Rooney. He has made no secret of the fact that he wants to leave Manchester United, and the club’s apparent unwillingness to ink a new deal should see him moving on this summer.
It’s one thing to have a fit, content Rooney on your side. It’s quite another to have an unhappy, affronted one.
Perhaps under Jose Mourinho’s tutelage, Rooney will blossom again as Chelsea’s first-choice striker, recapturing the deadly form that we know he is capable of. For England’s prospects in a World Cup year, that can only be a good thing.
Aged 27, United can still command a decent transfer fee for Rooney—even though the club insist the striker is "not for sale," as noted by Jamie Jackson for the Guardian.
The Rooney saga has the potential to become very messy and the player must now write a written transfer request if he wants to leave the club.
Should Chelsea table another offer for the striker, with Mata the makeweight in the deal, United should not think twice.