The 27-year-old Frenchman has been on trial in the Granite City and he has done enough to impress manager Jimmy Calderwood.
He will now sign on the dotted line in the coming days after agreeing terms.
Bossu has been looking for a new club since leaving League One Walsall earlier this summer.
Bossu has extensive experience in England after signing for Barnet from Lens in 2000.
Since then he has had spells with Rushden, Gillingham, Torquay, Oldham, Darlington and Accrington.