The Lithuania international spent last season on-loan at Valencia.
"We'll see later on if this is a bargain," said Lazio president Claudio Lotito of a proposed two-year contract for the player.
"We have not yet deposited the contract. The arrival of the French striker does not mean we have to sell one of our existing forwards. If we do, it's purely to keep the squad numbers under control and not financially.
"We have not received any offer for Mauro Zarate and he is not on the market. If a player tells me he wants to leave, then that's another matter, which is what happened with Stephan Lichtsteiner. But it requires the right offer."