The online snipers reckon Duke has taken a step back, but the 30-year-old ex-Western Sydney Wanderers skipper is having none of it, declaring he is more than happy with his decision to shun the A-League, Europe and Qatar or J2 Fagiano Okayama.

"There are people on social media platforms saying 'how can he expect to play for the Socceroos when he's gone to J2'?'' Duke gold FTBL.

"Why would he go when he could easily come back to the A-League as a marquee?

"Those sorts of comments are from people who are uneducated on how good the level is here. 

"I had options in Belgium, Germany's second league and Qatar but I had a few things to weigh up and I wanted to be in a league that worked so that I could spend Christmas and New Year with my (UK-based) family.

"I could easily have gone to Australia and signed a two or three year deal as a marquee but know the level in Japan."

Duke believes J2 is reminiscent of the Championship in England and will keep him in prime condition to continue his recent Socceroos fairytale.

"I don't have to justify my decision to come here, but I will say it's a quality league and reminds me a lot of the Championship in terms of its intensity and competitiveness," he explained.

"It will keep me at the level where I can still contribute to the national team. I'm not missing out on anything."

Duke is keeping Australia's established attacking order on their toes as coach Graham Arnold's go-to game-changing option off the bench.

His value was exemplified earlier this month when he struck Australia's third in their 3-0 World Cup thumping of China - his fifth goal for his country in just 11 appearances since his debut in 2013.

Call him a standby, stand-in or understudy - Duke isn't bothered, so long as he stays in and around a Socceroos side which Arnold has guided to 10 straight World Cup qualifying wins heading towards the anticipated October 7 clash against Oman in Qatar.

"To be fair, I think I'm in the best place mentally and physically that I've ever been," Duke added. "I think you can see that out on the pitch.

"I'm nipping at the heels (of Adam Taggart, Jamie Maclaren and Mathew Leckie) and I'm pretty happy with my goals to games ratio with the national team so far.

"It's been a bit of a whirlwind year, moving from Western Sydney Wanderers to Saudi Arabia (Al Taawon), which was a bit of a disaster.

"But it's also been a blessing in disguise when I look at where I've ended up now.

"I hated it there - I was playing out of position as a winger. I decided to up and leave and return to (Western Sydney) Wanderers, and I did well there.

"I got back in the national team for the Kuwait camp (in June). I played three games there and scored two goals.

"There was the Olympics (as an overage call-up) and I played twice there, got my deal in Japan and then of course the latest Socceroos camp. So a lot has happened in a short space of time.

Duke has scored once in five appearances for his new club, who are sitting 13th on the J2 table 30 games into the season.

"They're traditionally a top half of the league team but have been missing a few ingredients this season," he added.

"They're really focusing on next year, which is why they have brought me in, to try and put another piece of the puzzle together to try an get back to J1, and I'm sure there will be more signings.

"I know this league (and J1) from my time here before with Shimizu S-Pulse."