The 28-year-old Spaniard joined the Reds for €12million (£10.1million) two years ago from Espanyol, but his Anfield career never got going.
He was frozen out last season after openly criticizing then manager Rafa Benitez, and new boss Roy Hodgson is expected to let him leave the club.
Greek outfit Olympiakos are set to sign Riera in a deal worth €6million (£5million), with Liverpool receiving €4million up front and an additional €2million if Pireaus win the league next term.
Manager Lienen says the Spaniard will sign unless there is a major turnaround. He said: "Unless there is a major surprise then he will be our player.
"He is a great player who has proven his worth both at club level and for the Spanish national side."
The Spaniard played no part in Wednesday night's friendly draw with Grasshoppers in Switzerland as discussions over his future are continuing with the Greek side.
"Albert Riera did not play as a precaution because negotiations are ongoing with Olympiacos," said Hodgson.