Excitement among supporters was high when Mata stepped out of a helicopter and signed for United in a £37.1million transfer from Chelsea in January.
The Spaniard had an instant impact at Stamford Bridge, but he has made a steady rather than stunning start to life at Old Trafford.
Mata has only tasted victory once since his move to the north-west, but he has set Robin van Persie up twice in the three matches he has played.
Rooney is convinced United have signed a true star in Mata, though, and he is looking forward to the prospect of playing alongside the Spaniard and Van Persie on a regular basis.
"It's exciting," Rooney said. "Juan has come in and it's another world-class player to have in the squad. It'll take time - it can always take a little bit of time for every player to gel and to bond but we really hope we can all start scoring goals and help the team be successful."
A 0-0 draw at Arsenal on Wednesday put a further dent in United's Champions League prospects.
Moyes' men sit 11 points behind fourth-place Liverpool but one advantage they have over their rivals is that they now have an eight-day wait until their next game against Crystal Palace.
Moyes has decided to take his squad to Dubai for a warm-weather training camp during that time and Rooney feels the trip will be a big help ahead of a crucial run-in for the reigning champions.
"It's nice to spend time together," the striker said.
"When you're at home you go to training then you go home and see your families, but with trips like this you're training then spending time with the lads. It's good for us all to be together.
"It's a different environment for us and hopefully we can get some good training sessions in so we come back ready for the Palace game and the start of the Champions League.
"We've got a lot of massive games in the Champions League and the league. We're all looking forward to them."
Had Van Persie been more clinical, United would have headed to Dubai on the back of a win, but Wojciech Szczesny's brilliant second half save meant both teams took home a point.
Although the draw meant United lost ground in the hunt for the top four, Rooney hopes the result at the Emirates will give Moyes's men some momentum in the coming weeks.
"Coming to Arsenal any time and getting a point is always a good result," Rooney said.
"You have to take confidence from it. We've been stop-start for most of the season, but we hope we can build on this.
"We have a bit of a break before our next game now and hopefully we can prepare well and kick on for the big matches coming up."