The Red Devils look set to announce a deal for the Spaniard in the coming days after a shock deal between the Premier League rivals was confirmed.
Mata’s arrival is likely to throw Kagawa’s future at Old Trafford into further doubt, with the playmaker likely to be in direct competition with the new arrival.
The Japanese ace has already struggled for first-team action this season and could see his role further diluted by David Moyes, who appears not to favour the ex-Borussia Dortmund ace.
The 24-year-old has already voiced his displeasure at his current situation this season, and his unrest has alerted Atletico.
The high-flying La Liga side are keen to add Kagawa to their ranks in a bid to stay in the title hunt after an excellent start to the season.
They are hopeful that United will not block a move for the Asian superstar, which could be launched before next week’s deadline passes.
The playmaker is desperate to represent his nation at the World Cup, and knows that he must be playing regularly to guarantee his place in their starting XI.