Fans' fever is rising ahead of the big kick-off in the Eternal City as one side's most iconic player is ruled out of the capital's big Serie A clash on Sunday night
Totti will miss the game because he has not recovered from a thigh injury sustained in the 3-1 win over Atalanta two weeks ago.
Reja believes the captain's absence could have a negative effect on Roma as the build-up intensifies ahead of kick-off.
"I am sorry that Totti will not be there as it is an important derby. It's a shame." Reja told ANSA.
"Totti is a player with great class when he plays."
Emotions usually run high in the derby, and it is no different for the coach.
"I am living these moments with great intensity," added Reja.
"I feel in debt with the fans because I have not given them the satisfaction they deserve. I hope that we can do well during the game."
Lazio have lost their last four league matches against their city rivals.
Kick-off at the Stadio Olimpico is at 20.45 (CET).