Mata signing 'the first of many' - Moyes
Chelsea's Spanish midfielder Juan Mata holds the ball up during the Premier League Stamford Bridge in London on December 26, 2013 - by Olly Greenwood
United completed a move for Mata on Saturday for a reported fee of £37.1 million ($61.2 million, 44.8 million euros), eclipsing the £30.75 million that they paid Tottenham Hotspur to sign Dimitar Berbatov in 2008.
Moyes hopes that Mata will help to transform a desperate season that has seen the reigning English champions fall 14 points off the pace in the Premier League and crash out of both domestic cup competitions.
United have also reportedly opened talks with striker Wayne Rooney over a new contract and Moyes says that efforts to improve the squad will continue over the months ahead.
"This is the first, and there will be many more to come in time. I want the quality of Juan to be the start of it," Moyes told United's in-house television channel, MUTV.
"I don't think we will have any more (new signings) in January. I'm still working on it and looking to do so.
"But hopefully it will be the first of some new signings, some new players who will arrive, more likely in the summertime."
Mata arrived at the end of a week that saw United beaten 3-1 by Chelsea in the league and dumped out of the League Cup in the semi-finals by Sunderland, and Moyes said it had improved the mood at Old Trafford.
"Undoubtedly we could all do with a bit of a lift," said the Scot.
"We have not done as well as we would have liked to do. We see this as the start, we have to look to improve, and I'm going to try to bring in some new players to make that happen.
"I want to build an exciting team, I want to win and I want to give the supporters something to shout about. I've not done that often enough."
Mata, 25, could make his United debut as early as Tuesday, when Cardiff City visit Old Trafford in the Premier League.
The Spain international fell out of favour at Chelsea following Jose Mourinho's return as manager last year, but he expressed surprise that he had been allowed to leave Stamford Bridge in the middle of the campaign.
"To be honest, I think it's a bit surprising, but I have to say I am really grateful to Chelsea -- to the owner, to the people working in the club, and to the fans," Mata told MUTV.
"The last six months were difficult for me. I didn't play as much as I wanted to. I understand that football is a team sport and I respected that situation.
"But the chance to come to Manchester United was a great chance for me to carry on with my career. They are a massive club."