I don't think the club discussed Lookman's want to leave the club before the Super Cup final against Real Madrid. Atalanta played an incredible game against Real Madrid, drawing in the first half but failing to handle the pressure and conceding two goals in the second half, Atalanta's performance wasn't as good at the beginning of last season as they had at the end of last season, they seemed like they had a difficult time starting the season, Atalanta's beginning this season was different from last season's, and they won the Europa League last season, I have no idea why Lookman decided to leave, perhaps he wants to play for another big team rather than staying this season.
Atalanta's problems are even more difficult now that Scamacca's injury has put him on a long layoff with an ACL tear, Koopmeiners wants to be at Juventus and now there are rumors Lookman could leave which makes things even more difficult.
These are issues that could see Atalanta suffer in terms of performance at the start of the season especially as some of the players currently being talked about are core players who will be difficult for Gasperini to replace quickly.
If the situation continues to drag on then surely this will interfere with their performance even though in the first week Atalanta could win with a landslide score where 4 goals were created but still when there are internal player problems then this can spread to performance later.