According to transfer expert Ian McGarry on the Transfer Window Podcast, an unnamed Saudi club has made an approach for Mata.
Mata, 32, is out of contract next June and could be tempted by the money on offer from the Middle East.
McGarry explained the Saudi interest and where it is current at.
“It’s our understanding that the offer that Mata has is worth around $15m net per year to go and play in the Saudi Arabian league,” he said.
“It’s not at this moment in time that Manchester United have entered negotiations, we can’t disclose the name of the club at this moment in time.
“But we are certain that the offer is there. His father, who is his agent, is confident that Manchester United would release Mata on freedom of contract after he had his contract extended by the optional year in his current deal over the summer.
“Mata himself is yet to commit; however, at those kind of numbers you would have to think he would be tempted.
“It certainly is the case that Saudi Arabia is desperate to promote itself as a footballing nation as we know, as well as being a place where players can earn an extremely high amount of money and it would be tax free.”
Mata has been at Old Trafford since January 2014 when he arrived from Chelsea for a then club record £37.1m fee.
The Spain international has made 257 appearances for the Red Devils, scoring 50 and assisting 45 goals.