Fillol spat at Stringer during his side's victory in the Amlin Challenge Cup quarter-final on Saturday.
The player attended a hearing in Dublin today and pleaded guilty. An independent panel downgraded the ban from 26 weeks after taking his "genuine remorse" into account.
A statement on the European Rugby Cup website said: "The Judicial Officer found that Fillol had spat in the face of Stringer and that it had been an intentional, deliberate and grave act.
"He determined that the act warranted a top-end entry point from the IRB's Sanctions for spitting and considered that 26 weeks, from the available range of 11 to 52 weeks, was the appropriate entry point."
The ban will not include pre-season matches, which means that Fillol will be unavailable until August 12.