City make their eagerly-anticipated first appearance in Europe's elite club competition on Wednesday as they host Italian side Napoli, who finished third in Serie A last season.
With German giants Bayern Munich and Spaniards Villarreal also alongside them in Group A, Mancini believes his side have their work cut out despite their outstanding form this season.
The Italian said: "I think it is an exciting day for the club.
"To play in the Champions League after many years is very important, it is a special day.
"But I think we took the harder route in the Champions League.
"In this group there are four teams who can win the group or finish in fourth position. It will be very hard for every team."
Few teams can have entered the Champions League for the first time with so much expected of them.
After three years of heavy investment, City are on a mission to establish themselves as one of the continent's top clubs and their performances this term suggest they can make a big impact.
Mancini is comfortable with such expectation and, with plenty of Champions League experience in his squad, does not believe players will be burdened by pressure either.
He said: "I think this is normal for us.
"Now Manchester City are one of the best teams in England and Europe.
"For us it will be very important to do our job very well in this group.
"Tomorrow [Wednesday is the first game - the first game is always a difficult game.
"Napoli are a good team, last year they did very well in the Italian championship.
"Several of their players have been capped for their national teams and (Walter) Mazzarri is a very experienced manager.
"I expect Napoli to be a challenge but a lot of our players have played in the Champions League and I don't think they will feel pressure for this game."
While City are playing in Europe's top club competition for the first time since the 1968-69 season, Napoli are also enjoying a resurgence of their own.
The Partenopei, who last played at this level in 1990-91, were promoted back to Serie A in 2007 and have finished sixth and third since Mazzarri took charge two years ago.
Mazzarri, 49, said: "I live in Naples and can see how people feel.
"It is our fifth year back in Serie A. Now we are getting into the Champions League and not through the back door.
"The players have done a lot to bring the team to this level. Both the technical staff and I are very proud."
Napoli's last visit to England ended in disappointment, however, after Steven Gerrard struck a late hat-trick in a 3-1 Europa League defeat at Liverpool 10 months ago.