The veteran Irishman says he is heading Down Under to patrol the flank for his new club, meaning there could be stiff competition for places in the final third next seasonMelbourne City to play as an 'out and out winger', but will happily perform any role assigned to him by head coach John van 't Schip.
Duff this week became the latest big name to join the rebranded A-League franchise, signing a one-year deal after leaving Fulham at the end of last season.
The 35-year-old veteran no longer boasts the pace of his Blackburn Rovers and Chelsea heyday, but remains confident he is capable of making an impact from wide positions.
"I still think I can do the touchline role, getting chalk on my boots," he told Irish radio station newstalk.
"I think as you get older that's where a lot of players do end up, going further infield. Maybe because you've lost a yard of pace. For now I'm happy being a winger. Maybe the manager might see different further down the line. That's what I'm going as, an out and out winger."
Duff has operated in a central attacking role for the Republic of Ireland in the past and also seen action in midfield for Fulham in the latter stages of his impressive career, equipping him to perform a number of roles for his new club.
"When you're playing infield you've got licence to roam around more and (get) the ball," he said.
"Being on the wing, sometimes you can go 30 or 40 minutes without hardly touching the ball. When you're playing in the hole or the midfield you can get involved in the game. But it's not up to me, I don't pick the team."
Regardless of where Duff is used on the field, he will have the chance to link with a world-class talent in the form of Spain's David Villa, who will spend the first half of 2014-15 on loan in Melbourne before linking up with his new club New York City FC.
"I'm definitely excited to play with David Villa, he's been an amazing player for quite a few years," he said.
"You just have to look at his CV to realise what a top player he is. Also to play with the rest of the lads and to meet them. It's a totally new way of life over there. I'm just so excited about it. That's the reason I went, for football reasons. I'm not going for a holiday."