David Moyes promises to sign best in the world for Manchester United

David Moyes believes that Juan Mata is an important piece in the "jigsaw" that is his rebuilding job at Manchester United but he admits he urgently needs a central midfielder and left-back. Mata is in line for his debut against Cardiff City at Old Trafford this evening.

"The message this sends is that we're going for all the best players in the world at Manchester United and Juan is one of those players,'' Moyes said. "He's a top Spanish player, a top Premier League player and if you asked any Premier League supporter, no matter what club they support, they would be an admirer of Juan.

"I've got a big job to do here and a couple of new signings isn't all that's needed. There's a bigger job to be done but you have to start somewhere. If you asked me what I needed most, I would have said a central midfielder, I could do with a left-back, but sometimes you don't always get the pieces of the jigsaw at the time.

"I wasn't sure those pieces of the jigsaw would fall for us in this window. I hoped something would come up in this window that we wanted, and thankfully we got it. He plays for Spain, he's played in big games already for club and country.''

However talented, a 37 million pounds recruit from Chelsea cannot solve all United's ills that have caused them to tumble out of the domestic cups and lie seventh in the Premier League (although progressing well in the Champions League).

"No he can't but what it will do is help improve results,'' Moyes continued. "We've had a problem at Old Trafford making and scoring goals [14 Premier League goals at home, 22 away].

"If you look back at our record this season, that's been our biggest downfall. It's not necessarily been about conceding goals or how we've been away from home. It's just that when we've been at Old Trafford, we've tended to not be as clinical or make as many opportunities as we would have liked."

Mata can unlock defences with a pass. "He was a type of player we didn't have,'' Moyes continued. "Chelsea have got several players of his type in a way. I thought we could do with adding one of those kind of players. We need people to make more goals, and if he can chip in with them as well, then great. We're looking for his productivity.

"Juan has come to play three positions - off the right, off the left and behind the striker. He gives me a lot of flexibility and I certainly don't have any problems at this moment in time concerning how I play him. We could have done with him in the last month or two, when we've been without Robin [van Persie] and Wayne [Rooney]. If I'd had Juan in that period, I'd more than likely have had better results.''

Mata voiced his delight at the prospect of playing alongside Rooney. "For me, he is one of the best players in England,'' the 25-year-old said. "He is unbelievable; he can score, he can assist and he can take the ball in midfield. I will enjoy playing alongside him a lot. I will try to connect with him as much as I can. I will try to find the gaps between midfield and defence because that is something I was used to doing last season. That is the best position for me to play; to try to assist the strikers.''

Mata's presence at Carrington, arriving on Saturday, and already training twice, has given Moyes's players a lift. "I've seen it already,'' the United manager said. "One or two of them have said to me, 'What a great signing and we can't wait to play with him'."

Moyes felt Mata's arrival was different to Van Persie's impact last season. "The difference with Juan is that he's young. We've got Juan for a long period here. We hope, all things being well, he will be coming into his best period in the next four or five years, so that's what we've got to look forward to. I actually think there will be more clubs selling to each other [in this kind of deal] in the future, because a lot of the main players are at the big clubs now.''

United know they have signed a special ambassador as well as an exceptional player. "He's a real gentleman,'' Moyes added. "He arrived on Saturday, extremely smart, turned out well, incredibly polite, did all the right things and said all the right things.

"David de Gea was telling me what a good lad he is, but most importantly of all, we've brought him to be a player here and we know he is just that. With some of the footage of him we were looking at, it seemed half of the goals he's scored have been against Manchester United, so maybe that's another reason why we're glad to have him here!''

Qualifying for the Champions League is crucial. "It's imperative,'' Moyes said. "But I think players will still join Manchester United for what the club stands for, what's it's been, its history, the players who have come through here.

"Players look at Manchester United as a bit of a pillar of football clubs. All around the world it's recognised as being the biggest and best football club. So Champions League football is very important. But in the same breath this club has got its own standing and it can carry that."

Mata acknowledged and accepted that Champions League challenge.

"It is very important for us that we finish in a position that enables us to play in the Champions League next season,'' said the Spaniard, who won the competition with Chelsea.

"I like pressure. It's good when people are expecting big things from you. I am looking forward to try and make all these amazing fans happy."

One of the reasons he moved was for regular football, giving him a better chance of proving to Spain's coach, Vicente del Bosque, that "I have to be there" at the World Cup this summer.

"The last six months were difficult because I didn't play as much as I wanted but I respect that. Jose [Mourinho] is a very big, very good manager. It was a good lesson for me not to play at Chelsea, it helped me learn more about football, it helped me to become stronger and deal with life."