The former Blackburn Rovers and Chelsea man has met his new colleagues and launched himself into preparations for the 2014-15 campaign
Duff, 35, has signed a one-year deal with City and together with Spanish national team star David Villa – who has inked a 10-game guest stint – is one of the big names at the newly rebranded club (formerly Melbourne Heart).
Villa will arrive later in the pre-season but the Irish winger has now had his first taste of action with his news colleagues.
The A-League outfit arrived in England on Tuesday this week and by Wednesday had their first session at majority owner Manchester City's Carrington Training Centre.
John van 't Schip's squad had a pool session followed by a first training session on English soil. The session commenced in the late afternoon with Manchester City's first-team having used the facility earlier in the day.
Melbourne City are in town for 17 days to train at the Premier League champions' base and to play a series of pre-season friendlies ahead of next month's Westfield FFA Cup round-of-32 clash with Sydney FC on Tuesday August 12.
It's been a big few days for the club. They flew out from Melbourne on Monday night after announcing a five-year sponsorship deal with Etihad Airways as well as launching their new home and away kit.
City's 2014-15 A-League campaign begins away to Sydney FC, with a highly anticipated Melbourne derby against Victory at Etihad Stadium on October 25.
The new Hyundai A-League season kicks off on October 10. City will host Western Sydney Wanderers in round one.