Atletico is playing a high-stakes game here, never before have they dabbled in this sort of territory when it comes to transfer fees.
He could well be the second coming of Griezmann and probably even better but at that age with that sort of price tag it no doubt represents a huge risk for them. If this doesn't pay off like they hope it will I can see them really struggling to pull in capable players in the future.
Considering the team is going through a thorough rebuild from their golden era this could absolutely mean boom or bust for them. Atletico doesn't have the same security to back up their financial muscle as the super clubs have.