The 26-year-old ended the campaign on a high note for the Red Devils despite their disappointing season as he notched six goals in his final six games.
Mata has admitted that he has a lot of work to do over the next few months with Vicente del Bosque's side in Brazil, and with United as they try to re-establish themselves as one of the top clubs in the Premier League.
He told Laureus.com: "The last three or four months for me were great. I played a lot. I scored some goals. So I am looking forward to being there and to try my best for the team.
"It's been a difficult year, but I think this season we will improve and we will try to win again, because Manchester United is about winning and fighting for titles."
Spain get their World Cup campaign underway on June 13 against the Netherlands.