Roma sporting director Monchi says Atletico Madrid rather than Chelsea are his club's biggest rivals for a place in the knockout stages of the Champions League.
Roma host Atletico on Tuesday while Chelsea are at home to Qarabag in Group C's other match.
Azerbaijani side Qarabag will be Roma's next opponents before their double header with Antonio Conte's Chelsea, but former Sevilla sporting director Monchi said Atletico represent the toughest task.
"We are going to face an Atletico like we have seen in previous years," he told Spain's Movistar Plus. "They work very well. They're physically strong, they have speed. They know what they have to do and are a team who know the tempo of the game perfectly.
"I think it's the most difficult rival in the group. In my opinion, Atletico are more complicated rivals than Chelsea. They've been working together for three, four, five years, with the same coach, using the same system and without changing many players -- practically nobody this year. This is why they're really fearsome opponents."
He added: "Let's hope we play a great game and, obviously, that Roma emerge triumphant."
Roma have won only two Champions League games since 2010 and failed to qualify last year when beaten 3-0 by Porto in the playoff.
However, Monchi told Cadena Ser radio that he "wouldn't sign for a draw" against Atletico on Tuesday.
"We have to be ambitious," he said. "It's a very level group and it's crucial to start with a win. We are going to try.
"Atletico have reasons to be ambitious. Besides Real Madrid, they are the most regular team in the Champions League, having reached two finals and one semifinal in recent years. I'm not surprised by it.
"I've known [Atletico coach Diego Simeone] for a long time. We were teammates at Sevilla for two years [1992-94]. He transmits that ambition to his team and his players reflect that perfectly on the pitch."
Roma have had a summer of change, with Monchi arriving along with coach Eusebio Di Francesco, while Francesco Totti ended his long playing career at the club to become a director.
"We are trying to build a project not just for the present but for the future," he said. "We have a coach, Eusebio Di Francesco, that we trust a lot.
"We've had important changes in the team with players that last season had a specific weight on the side leaving like [Mohamed] Salah, [Antonio] Rudiger and [Leandro] Paredes.
"We've signed new players that we think in the future will be important.
"There has been a crucial change to the team and that is Francesco Totti's retirement. This is the first year since Totti stopped playing so it's a new Roma, but just because it's a new Roma it doesn't mean it's less solid.
"I think the team is gradually growing and we are on the right path.
"I'm learning a lot from Totti. There is no better teacher than him to get to know Roma. We have a very good relationship. He is happy, he likes the role that he has because it allows him to be close to the team, to the technical staff.
"He's got a good relationship with the majority of the players because he knows them well and with the coach because a long time ago they were teammates [Di Francesco was a member of Roma's 2001 Scudetto-winning side]. Totti is helping me a lot. He feels useful and important. I think he can bring a lot to the club."
ESPN FC's Spain correspondent, Adriana Garcia, contributed to this report.