If they can maintain and improve it to be even better, then it is not impossible that they will become a very dangerous team in the Champions League. Atalanta has the capital for that, they just need to improve it again.
Indeed, they must, ya, they must do more efforts and consistency in order to be able to compete very well in UCL, because, all clubs are here selected from top clubs in each league. Atalanta, made not much changes in their squad, so their solidity should be change very much.
Anyway, now, we have started leg 1 play-off Champions League.
From some of those that have played, LOSC caught my attention.

Goolge/losc-vs-slavia-praha
LOSC won 3 - 0
So I am very sure that they will win, because in the second leg, their opponent, Slavia Praha must score at least 3 goals without reply, or even more if they want to secure their position and enter the qualification. But it seems like this will be difficult. Because LOSC is currently quite good in their progress, as well as their performance progress in Ligue 1.