The Ethiopian-born Dutch star had been in limbo about his future for months, with the Wanderers in no hurry to extend the current A-League deal which expires at the end of this season.
Hersi confirmed he'd finally put pen to paper and The World Game understands the 31 year-old will not be at Wanderland next season.
"I know a lot but the media don't know yet," he said.
"I will tell you one day but now is not the time to tell because we have a big few weeks coming up and if the right time is there I will tell you."
Hersi has been a revelation since joining the Wanderers in their inaugural season.
The livewire winger played an integral role in the club's remarkable maiden campaign and has continued to light up the pitch as he weaves in and out defences with his crafty footwork.
He'd had almost two years out of the game with a knee injury before joining Western Sydney and credits the A-League club for reviving his career.
In perhaps a hint he may be leaving, Hersi spoke almost reminiscently about his time at the Wanderers.
I've had a good two years here .... and it's fantastic what this club has achieved and what I've achieved with this club," he said.
"It's been something new for me in Australia and I like it but we'll see what happens at the end of the season."
Hersi was part of the Wanderers side which lost to Newcastle Jets 2-0 last week in what was an unusually insipid display from the premier.
He insists his focus is solely on Saturday's derby against Sydney FC and the AFC Champions League game away to Chinese side Guizhou Renhe next Wednesday.
"We're just thinking about the derby now then we have China so it's a big two weeks," he said.
"That's what's most important to the club and me as well because it's a new experience for me to play in the ACL."