As another fine campaign between the sticks comes to a close, speculation continues over the 26-year-old swapping Old Trafford for the Bernabeu this summer.
De Gea, United’s Player of the Year for the past three seasons, was set to join Madrid in 2015, only for his transfer to collapse acrimoniously on deadline day.
Madrid are said to have the Spain goalkeeper in their cross hairs once more, but Mata is hopeful his compatriot and team-mate will stay put.
“Well, I think he is happy and I think he is obviously committed to the club. He has got a contract,” Mata said.
“He is obviously more than used to living England, he is happy in Manchester.
“For me, he is great – great person, great player. If not the best goalkeeper in the world, top three for sure.
“He gave us a lot of points during the last seasons, player of the season for the team, and obviously he is happy and I don’t see a reason for him to change. So let’s hope that he can save so many more goals for us.”
De Gea is set to return to the starting line-up at Tottenham on Sunday, when United will be without Zlatan Ibrahimovic, Luke Shaw, Marcos Rojo, Ashley Young and Tim Fosu-Mensah through injury.
Marouane Fellaini is suspended and nobody could blame Paul Pogba for missing the match after his father Fassou Antoine passed away.
Mourinho has underlined his intention to rotate his players in United’s final three Premier League matches given a top-four finish is likely beyond them and their shot at Europa League glory looms large.
The May 24 final against Ajax offers not only the shot of silverware but a guaranteed Champions League return at the end of what Mata accepts has been a turbulent campaign.
“It was a big chance for Celta Vigo in the last second of the game,” he told CNN of John Guidetti’s last-gasp chance in Thursday’s semi-final second leg.
“Obviously I was thinking it was a goal, but luckily it was not a goal and we could get through to the final.
“I’m really, really, happy to bring a lot of United fans to Sweden, to Stockholm. Hopefully to celebrate with us.
“We had ups and downs (this season). We are not as high as we would like in the Premier League, but if we can go to the final and win the final, that means that we will play Champions League next season.
“Having won the Community Shield, having won the League Cup, having the chance to now win the Europa League, so let’s talk about it after the game hopefully with a smile on our face and saying it was a good season.
“Because if we can play Champions League next season and we won three trophies, that would be a great season.”