The Spaniard's four games for United since his January move from Chelsea have resulted in two draws, one defeat and just one win.
If it wasn't clear Mata couldn't single-handedly reverse United's fortunes before he arrived, it certainly is now.
It's something that's not lost on the 25-year-old, who told the Manchester Evening News that he expects United to spend in the summer.
I don't know what will happen in the summer but the manager said the other day at a press conference that he's going to be signing players.
I think this club is at a stage of change, but I can tell you that the best players in the world will always arrive.
United have already done the hard part.
With the prospect of a season without Champions League football looming like a dark cloud, David Moyes managed to convince Mata that Old Trafford was the place for him.
Moyes was helped in the negotiations by Jose Mourinho's reluctance to pick him at Stamford Bridge. But he still managed to persuade one of the world's best players—a World Cup and Champions League winner—to move to Manchester.
United and Moyes will hope it hasn't gone unnoticed.
Such is the size of the rebuild facing the United manager in the summer, Mata is expected to be just the first to come through the door rather than the final piece of the puzzle.
And whether he knows it or not, he has blazed a trail. A trail for the players who might follow the same path at the end of the season.
Mata will hope, like most United fans, that Moyes can convince players of a similar calibre to be part of a new era at Old Trafford.
He will need to if this season is to be a blip rather than a sign of things to come.
And while Mata's words, his belief that the squad will be strengthened in the summer, are fairly meaningless, his actions are not.
One of the world's best players, about to hit his peak, has chosen to ignore the upheaval following Sir Alex Ferguson's retirement and join United.
And that will do more to convince others to follow than any public declaration.