Spanish outlet El Gol Digital (h/t James Walters of the Daily Express) reported the player will not sign a new deal to remain at Old Trafford when his contract expires at the end of the season. Los Blancos could then move for the Spain international as a free agent.
Mata has been hugely successful since moving to the Premier League in 2011, winning two FA Cups, two UEFA Europa Leagues and the UEFA Champions League during his spells with Chelsea and United.
The player began his career in Real's youth team before making his breakthrough with Valencia in 2007.
Mata won the 2010 FIFA World Cup but has found himself on the fringes of the Spanish squad due to a lack of playing time at the Theatre of Dreams.
However, his talent is undeniable, and a switch back to La Liga could be seen as a wise move as he enters the latter stages of his career.
At 30, Mata still has much to offer, and Solari reportedly views the Red Devils magician as a potential replacement for Isco.
SportBild (h/t Manolete of AS) reported Bayern Munich are keen on the Real attacker and could make a move to bring him to the Bundesliga.
Mata brings extensive experience with him and would offer Los Blancos a cheap option to strengthen the squad during a period of transition.
The reigning Champions League holders are only fourth in La Liga but are just five points behind leaders Barcelona.
The loss of Mata would be a blow to United, but manager Jose Mourinho has used him frugally since the Portuguese arrived at Old Trafford two seasons ago.
Mata remains a popular figure in the squad, but his lack of power and pace is an issue for a manager that favours a physical approach to the game.
The player reached the unique milestone of 50 goals and assists in the Premier League, with United defeating Fulham 4-1 in the Premier League on Saturday.
Speaking to MUTV (h/t Sky Sports) about his achievement, Mata said:
"It's not bad, 50 and 50.
When I came to the Premier League a few years ago I was very excited and very motivated about my period in the Premier League and I am enjoying it so much.
I am lucky to have been able to score and assist that many goals, but I am still hungry for more: I want more assists, more goals, more enjoyment in the pitch, so hopefully I can do (so)."
Mata's style suits La Liga more than the Premier League but the player has consistently risen to the physical challenges of English football.
Pep Guardiola's arrival at Manchester City has welcomed an increased technical edge to the domestic game, and Mata would remain a useful squad member if United can convince him to spurn Madrid's reported overtures.