Mata will make his debut in tonight’s Premier League clash with Cardiff at Old Trafford knowing his club have slipped six points adrift of a Champions League qualifying slot after an awful campaign.
The 3-1 defeat at Chelsea on January 19 was their seventh defeat of a season that has also seen them exit the FA Cup at the third round stage and lose a Capital One Cup semi-final to relegation threatened Sunderland.
It has led to a growing view that United are floundering at the highest level and are set for a period in the wilderness.
Moyes is not prepared to countenance that and while he accepts further big-money additions might have to wait until the summer, there will be some changes.
“I am not going to accept it,” said Moyes.
“I am disappointed we are not in a much stronger position. I am disappointed with how we have played.
“I, ultimately, take the rap for that.
“But what I will do is make it right. I am going to get better players in.
“Unfortunately, I don’t think there will be more in January. But it will change.”
The exit of Anderson on loan to Fiorentina, plus the impending departures of Wilfried Zaha and Fabio further confirm Moyes’ intentions.
It is impossible to see Rio Ferdinand’s contract being renewed given his recent lack of games, while the futures of skipper Nemanja Vidic and full-back Patrice Evra are also in the balance.
With Alexander Buttner, Nani, Ashley Young and Javier Hernandez among those who also have questions marks hanging over them, the Moyes revolution is under way.
“I have given every player the opportunity to play and show what they can do,” he said. “We have had a pretty good chance to have a look at it.
“The players have to perform. If they want to be here and making sure they have a jersey, they have to show it in the games.
“Undoubtedly, this club wants to be at the top. We want to be challenging.
“At this moment in time we have failed to do that. We want to do something about it.”
For now he is just happy to bring in some much-needed quality.
“There will be more players like Juan (Mata) in the future, I have no doubt about that but my gut feeling is that it will be the summer.”
For his part, Mata has branded Wayne Rooney one of the best players in English football history.
United officials hope Mata’s arrival can convince Rooney to sign a massive new contract extension, worth an estimated £300,000-a-week to further fuel hopes of progress after this season’s dismal fare.
It would certainly have Mata’s approval if Rooney did sign.
“I cannot wait to play alongside him,” Mata said yesterday. “He is one of the best players in the history of this country.
“He is unbelievable. He is a striker who can score, can assist and can come to the midfield to take the ball and move. I will enjoy playing alongside him.”
Mata, who elected to take the number eight shirt vacated by Anderson rather than the number seven many had predicted, is not giving up on United retaining their Premier League title even though his new club are 14 points adrift of pace-setters Arsenal.
“What I liked most about this club is the character,” he said. “If another club was in this position it would be very difficult for them to come back and take first in the league.
“This club can do it. This club is used to fighting to the end. This is the real image I have of Manchester United.”
Tonight’s game sees United legend Ole Gunnar Solskjaer return to his old stomping ground for looking to win points for Cardiff’s relegation fight.
He is certain to receive a good reception, with his playing days at the club from 1996-2007, under Alex Ferguson, fresh in the memory.
It is a situation he has previously imagined, but without thinking it might really occur before he began his managerial career with Molde.
The 40-year-old said: “It has not been an ambition but it has been sort of an unrealistic dream.
“The former manager just always installed into us ‘dream big’, and maybe unrealistic, because you never know it might happen.”
Solskjaer was also quick to dismiss the notion United no longer have the fear factor.
He said: “Of course the fear factor is still there. You’re going to the biggest club in the world.”