The high-profile Spanish midfielder has joined the A-League Men team ahead of the 2024-25 season on a one-year deal.
But Mata has not played competitive football in a year, last featuring for 10 minutes off the bench for J1 League team Vissel Kobe in September 2023.
The 36-year-old's last start across any league or tournament was in March that year when he was playing for Turkish club Galatasaray.
Mata, fronting his first press conference in Australia after receiving an airport welcome from fans early on Saturday morning, insisted he would be able to fire for the Wanderers.
After leaving Japan, Mata trained with a fitness coach in England before training with Danish club FC Nordsjaelland.
"I've been with this team dynamic (at Nordsjaelland) for almost two months and I feel good," Mata said on Saturday.
Juan Mata is eager to get onto the pitch for Western Sydney Wanderers. (Steven Markham/AAP PHOTOS)
"I feel ready to come back, really eager to be on the pitch. I feel good and confident that it's going to be a good season.
"I'm very lucky to have the career that I had, but I'm still hungry for more, to keep enjoying football, to keep hopefully winning trophies with this club now."
Probed about his one-game stint at Vissel Kobe, Mata said it was a "long story".
The attacking midfielder landed in Japan after featuring in the starting side only three times for Galatasaray in the 2022-23 season.
He was part of the Manchester United exodus under then new manager Erik ten Hag in 2022, leaving the Premier League club after scoring 51 goals in 285 appearances across nine years.
With United, Mata won the Europa League, FA Cup, League Cup and Community Shield.
He had already won the Champions League, FA Cup, Europa League and FA Community Shield between 2011 and 2014 with Chelsea.
His brilliant career also includes winning the 2010 World Cup and 2012 European Championship with Spain.
"That's kind of a long story. The team was doing really well when I arrived," Mata said of his Japan spell.
"We won the league at the end (of the season). When a team is winning, it's difficult to make some changes.
"It was frustrating on a personal level, not to get as much game time as I thought I would.
"With different stages in your career, it also makes you realise that you have to focus on keeping on giving your best."
Head coach Alen Stajcic is in no doubt Juan Mata will play a massive role for the Wanderers. (Steven Markham/AAP PHOTOS)
First-year Western Sydney coach Alen Stajcic, who joined the club in June, also shrugged off concerns around whether their latest signing could deliver.
"Someone of Juan's stature doesn't just bring something on the field, it's what he brings off the field," Stajcic said.
"To bring someone like Juan, it's not just a short-term thing. It's a legacy thing.
"To have his football insight, his experience is something that you just don't get that easy.
"He'll be able to impart that knowledge. He'll be able to impart his football skills to a new generation of Australian players."
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