So, thats mean psychotherapy from Simeone, it is very possible for Griezmann to return to his best performance for the club. If we look at the performance of athletico players last season, both in La-Liga and UCL, they have good confidence. I think Simeone's role is very crucial for the mentality of Atletico players. It is very possible that Griezmann will also have better confidence while at Atletico this season,
I think Simeone is a coach with good psychological impact on his player so he will be able to give a good therapy to Griezman.
Griezman will find fun when he plays in Atletico, not like in Barcelona. It is like his home, where he made his name as a star player. If he can come back to his best, Atletico will dominate La Liga and increase their chance in Champions League.
He's still capable of duels, I don't think he's going to be a substitute. Simone should have given him more playing time. It's a mistake for Barca to throw Griezman out, they don't have an experienced striker backing. Of course his move will make Atletico stronger because Simone has an alternative striker. Maybe he can be the key to athletico's victory.
He will start as a substitute in a few early matches. If he performs well, Siemone will order a main position for Griezman. It is funny again (like Suarez transfer) when Barcelona gives a point in the loan contract that allows Atletico to buy Griezman with huge discount after this season.