Actually I think if we get Griezmann, he would have the biggest chance of all of our recent signings to be a flop. Still not a big one, but the biggest one out of Coutinho, Dembele and him.
The questions I have about those 3 signings, if they all happen:
Coutinho:
How fast will he integrate into our squad, especially into the #8 role where he will be used the most?
Nothing else... he will be great here.
Dembele:
Can he stay injury free?
Can he learn to play with Messi (I think this is hard, because of Leo's free role and unpredictability...)?
Can he fulfill his defensive duties when playing RM in defence?
If he does these 3 things he will be a success here.
Griezmann:
Is he prepared to sit on a bench more?
Can he be motivated to play on the highest level again?
Can he learn to play with Leo?
Is he prepared to / Can play out of position?
Is he able to do the defensive duty while playing in front 3 with Leo and Luis?
Will he block Alba when playing LW?
Can he adapt to the possession style of play?
That are my concerns, but if he comes here, I think he will overcome them. In the end, he wants to win trophies, so I'm sure he is prepared to make sacrifices.