The Algeria winger missed much of the 2019-20 season with a ruptured cruciate ligament, returning just before the pandemic.
SPAL’s relegation to Serie B means Fares, 24, is available and Lazio have been pursuing him for a while.
Lazio and SPAL will hold a meeting this coming week to define the transfer, which will be worth about €10m.
A counterpart could be included in the deal, with SPAL admirers of Lazio forward Simone Palombi, 24, who has just returned from a loan spell at Cremonese.
The French-born player has been capped nine times by Algeria and represented them at last year’s African Cup of Nations.
Fares’ move to Lazio has finally been confirmed.
— S.S.Lazio (@OfficialSSLazio) October 1, 2020