The Romans head into the encounter second in the standings, three points behind Serie A leaders AC Milan and four points above Inter.
"To beat Inter would be an important step for us," said Reja. "It would bring enthusiasm and would be a big boost in confidence for my players.
"We will need to play a perfect game but the time has come for us to beat a big club."
Lazio have lost just once this season in the Eternal City, a 2-0 defeat to city rivals Roma back in November.
Lazio coach Edy RejaHowever, the Biancoceleste have struggled in recent weeks with draws at Parma and against Catania.
Reja has reason to be wary as Inter travel to the Italian capital on the back of last weekend´s 5-2 triumph over Parma.
The result was all the more impressive considering the Nerazzurri were without top scorer Samuel Eto´o through suspension.
The outcome ended a four-match winless run for Rafael Benitez´s men and lifted the team to fifth.
"Our focus is still on the scudetto," said Benitez. "The tournament is still long and the team is showing character."
Friday´s encounter in Rome will be Inter´s last league game of the year and the Nerazzurri are determined to finish on a high.
"Lazio are doing well but we want to play a great game in Rome," said Inter captain Javier Zanetti.
"Our only thoughts are on the game in Rome, we want to win because we don´t want to lose ground with the top teams in Serie A.
"Then we will think about the Club World Cup, which will end a magnificent year for us."
Victory at Lazio would be a big boost in confidence for Benitez´s men, who visit Werder Bremen in next week´s Champions League fixtures before making the journey to Dubai to prepare for the FIFA Club World Cup.
Inter are still without suspended Eto´o and injured Diego Milito, David Suazo, Julio Cesar, Maicon and Christian Chivu.
The hosts will be at full strength with defender Giuseppe Biava having shaken off an ankle injury. (espn)