Western Sydney Wanderers foundation coach Tony Popovic has sensationally quit the club just a week before the start of the A-League season to take on a job at Turkish club Karabukspor.

Popovic's current contract was due to run until the end of the 2017-18 season after re-signing for three years in mid-2015.

Popovic's WSW legacy Games coached: 174

174 Wins: 73

73 Draws: 40

40 Losses: 61

61 Finals appearances: five out of six seasons

five out of six seasons Asian Champions League winner in 2014

"Today's a very difficult day to hold this press conference. It's to pursue an opportunity overseas, that's basically what it is, and it's in Europe. I've always had the ambition to coach overseas," Popovic told a media gathering.

"I've been fortunate enough to have had opportunities in Asia. The club's well aware of [my ambition to coach in Europe], the timing certainly is not great, we don't plan these things, but it's come up very recently.

"It's an opportunity to get my foot in the door in Europe in a big competition, and that's where I'd like to take my next challenge."

Tony Popovic's resignation leaves the Wanderers in disarray just a week out from the A-League season. ( AAP Image: Dean Lewins )

Popovic said it's been "an amazing five years" at the Wanderers.

"Starting the club from zero, leaving Crystal Palace to pursue this opportunity, to see where this club is after five years, with a new stadium to come," he said.

"I leave a lot of special memories, some friends that I've made and amazing football staff that has always supported me with the direction we wanted to go as a football club.

"I'd like to thank all the players from day one. There's a lot of amazing people and players that have played here.

"I'm sure whoever comes in will have a fantastic foundation to be able to build and bring his own ideas and continue to make the Western Sydney Wanderers successful."

The 44-year-old was the Wanderers' first coach when they entered the A-League in 2012, and guided them to consecutive grand final appearances in their first two seasons of existence.

Popovic also steered his side to a famous win in the Asian Champions League final in 2014, earning him the AFC coach of the year award.

At about that time, Popovic was linked with a job at English Premier League club Crystal Palace, where he played more than 100 games.

He also reportedly rejected a move to Chinese powerhouse Shanghai Shenhua late last year.

Following a poor season in 2014-15, in which Western Sydney finished ninth, they bounced back with another grand final appearance in 2015-16 but again fell short in a 3-1 loss to Adelaide United.

Western Sydney hosts Perth in round one of the new A-League season next Sunday.

"Tony has been fundamental to this club's success and growth since our inception in 2012 and leaves a lasting legacy that this club will use as a platform to continue our rapid growth," Wanderers chief executive John Tsatsimas said.

"He will forever remain a great part of our history, leading us on our course to be globally recognised and respected as a football club.

"While we have always known Tony was destined to have a great future coaching on the global stage, just as he did as a player, we are sure he will look back fondly on his time with the Western Sydney Wanderers with pride in the achievements we have made as a group."

ABC/AAP