Totti finally hung up his boots at the end of last season at the age of 40, having played his entire career at the Stadio Olimpico.
The playmaker made 786 appearances for his boyhood club, scoring 307 goals and establishing a reputation as one of the most talented footballers of his generation.
And while he was not such a force on the field in his final seasons, Conti still believes he is missed sorely at Roma.
"It has been hard for us, it would be like speaking about Barcelona without Messi, he gave everything in his final years," the former winger, who lifted the World Cup with Italy in 1982, told Goal.
Roma now face an uphill struggle against Messi and Co. having fallen 4-1 in Wednesday's Champions League quarter-final first leg.
And Conti affirmed that if they cannot cut out the mistakes that cost them dear at Camp Nou they can forget about the semis.
"A comeback? It is very tough, Barcelona tend to play always the same way, keeping control," he added.
"But they also won thanks to many of our own mistakes, they are still the best team in the world and we can't afford these any more mistakes.
"[Coach Eusebio Di Francesco] will speak about keeping calm, football is a sport in which you can do in two minutes what you didn't in 70 and if Barcelona score first, that should provide more motivation."
Roma and Barcelona lock horns in the Stadio Olimpico on Tuesday, with the club from the Italian capital looking to reach the last four for the first time since 1984, when they eventually lost out to Liverpool in a penalty shoot-out.