Heskey flew into Australia on Friday morning and joined his team-mates for an informal training session on the Hunter Stadium pitch later that afternoon after charming the media at a packed press conference.
"My fitness is not too bad. I have been doing a bit with (Wigan's) development group, their Under 21s - they are young lads and they keep you fit," Heskey said.
"But I haven't played any games and everyone knows match fitness is different to training every day.
"But I spoke to everyone here and we will be working towards that first game.
"That is what we will be building for to see if I can play. I am here to play."
Heskey decided to head to Australia this month having left Aston Villa, following a career that had also taken in Leicester, Liverpool, Birmingham and Wigan.
He scored seven goals in 62 appearances for England.