I would say that Ademola Lookman has literally been unlucky with the transfer window this summer because first he was linked to Inter Milan, then Spurs, Bayern Munich, Arsenal and no one was successful. Staying at Atalanta is the only option at this moment and I doubt if he will be happy playing for the club for the rest of the period.
It is quite possible that by winter one of these clubs will decide to strengthen (or simply increase the depth of the squad/variability) and will still buy him, so it is probably too early to talk about an unsuccessful season. If this does not happen, then of course I would be very unhappy in his place, Atalanta will definitely not be in contention for anything this season, they have seriously weakened due to their actions in the transfer market.