Barcelona activated Griezmann's release clause of €120million to land the Frenchman, but the striker has struggled to recapture that form that made him one of the most devastating attackers in the world,
While Griezmann has enjoyed decent returns this season, Mathieu feels it was a mistake for his fellow Frenchman to swap the Wanda Metropolitano for Camp Nou.
“Griezmann is not at his Atletico level. Personally, in my opinion, it is a mistake that he came to Barcelona. At Atletico he was a very important piece and I don't know if he has that importance at Barcelona," he told RAC1.
The 29-year-old has only managed to score 27 goals in 82 appearances in all competitions for the Catalan giants, and while he has improved at club level, his form is still nowhere close to the displays he puts on regular basis for national country, France.
He will need to ensure that his performances go up a notch if Barcelona are to have any chances of winning a trophy this season, considering that they are currently placed fourth in LaLiga standings and lost 4-1 to Paris Saint-Germain in the round of 16 first leg of the Champions League.