Montella's men head to the Stadio Olimpico after a 1-1 draw at home in the first leg of the last 16 tie.
Roma are winless in four matches and have claimed victory in just three of their past 15 outings in all competitions.
But Montella is still wary of Rudi Garcia's men, who remain second in Serie A despite their form.
"I don't think that we will find a team on their knees," Montella said on Wednesday.
"I personally know some of their players and I know how good they are. We don't have to forget this and the fact that Roma is still the second team on the table in the championship.
"They are not only great footballers but also men with strong personality. I don't think that Roma's season is over yet, actually I'm sure that they will want to show that they can react to the last poor results.
"On the other hand we need to focus on our game without thinking to all these aspects."
Roma have just one win at home in 2015, but Montella does not believe that form favours his team at all.
"I don't believe that the fact that Roma is struggling at home can be an advantage for us," he said.
"I know football fans and how passionate are those [Roma] supporters in particular and I'm sure they will stand up for their team in such a difficult moment."
