Atalanta performance was also not very impressive in Serie A last season, but in the Europa League they were able to show their best side by beating the two strongest candidates to be champions (Liverpool and Leverkusen) before finally confirming themselves as champions. Atalanta may be able to spring a surprise in the UCL, but Arsenal will not be easy to beat in their current form.
All teams always try to win in every match, but differences in quality and other unexpected things can change the outcome of the match. The new format is a bit tiring because the number of matches will increase, the coach must be able to keep his players to always maintain their best performance so they can qualify for the next round.
I don't mean to underestimate Atalanta, but when compared to other clubs in the Champions League, there are several clubs above them in terms of strength, including Arsenal in my opinion which is slightly better than Atalanta. However, they are still a club to be reckoned with and anyone who faces them must be careful.
Last season in the Europa League was a real example when they managed to beat the strongest candidate to become champions. Almost everyone was not on their side, but in the match they were actually able to become winners, including beating a club that was unbeaten in all competitions last season.
On the other hand, the difference is that because the Champions League is different from the Europa League, here they will get more pressure, so they must be ready for that by improving their mentality.
This is not the first time that Atalanta is will be playing in the Champions league. They have been in the competition in previous times and they fully understand what it takes play in the Champions league. In my opinion any team that manage to win the europa league can cope with the demands of the Champions league. Atalanta did very well in the europa league last season, they even performed far better than some clubs that participated in the Champions league. The only difference is that here they will be playing with more bigger clubs that boast of more squad dept and experienced managers. But I believe that Atalanta can survive the group stages and even make it as far as the knock out stages. Atlanta is not the least club in the Champions league, I know it will be difficult for them to win the Champions league, but they are also a strong side that can win clubs with same ranking as them. Sometimes they can even win bigger clubs too. They did it against Liverpool last season, under Jurgen Klopp.