Roma have stuttered in recent weeks with four defeats in their last six games in all competitions, including a 4-2 defeat in France last week.
Spalletti bemoaned some lapses in concentration in that first-leg loss and acknowledged they must be better if they are to qualify for the last eight.
However, he remains confident Roma have the quality to complete an aggregate win and expects his men to put on a show in front of their fans.
"We can't afford to make bad decisions," he told a press conference ahead of Thursday's clash at the Stadio Olimpico.
"Qualification is there for us to reach out and grasp. We cannot be afraid. I'm absolutely convinced that our players will want to be the stars of the evening.
"My lads are very mature and they'll make the correct analysis and act accordingly. We'll need something extra.
"We had a bad result, but we have to see it in the right light - if we'd lost 1-0 then we'd still need to score two goals, so that's what the path is."
Striker Edin Dzeko, who scored in their 3-0 Serie A win over Palermo on Sunday, has urged his team-mates to step up their level and prove their quality.
"Everyone says we're a good side and I believe that, but we have to prove it," he said.
"Both myself and the whole team can improve, we all need to give a bit more than we have recently."