United finished sixth in the table this season – with the side failing to reach the top four in the last two campaigns.
Jose Mourinho’s men did qualified for the Champions League after winning the Europa League – after beating Ajax in Stockholm last week.
And Spanish midfielder Mata has complained about United’s consistency – with the Old Trafford outfit only scoring 54 times, the lowest in the top half, and drew 15 of their 38 fixtures.
He wrote in his blog: “We won the Community Shield right after the pre-season, we lifted the EFL Cup trophy in London, in a very special game for me, and of course the final in Sweden.
“But we are aware of our lack of consistency and effectiveness in the Premier League that prevented us from fighting for the title, which is what Manchester United is supposed to do.
“Personally, I have played over 40 games once again. It’s true that I was injured for a month and a half, something that had never happened before in my career, but at the end I was able to enjoy again what I like the most and I finished the season happy.
“I want more, of course, but I’m happy and proud of what we have done along the way. I hope that you have the same feeling, and that you are excited and really looking forward to the next season!”