The 29-year-old striker bagged 29 goals in all competitions for Sevilla last term as he helped them secure the Europa League title for a third straight year.
Gameiro made a €32 million switch to Atletico in late last month after enjoying great success with the Andalusians for three seasons. He plundered 68 goals in 141 appearances for the La Liga club.
Nonetheless, the Frenchman has explained that the dominance of Lionel Messi, Luis Suarez and Neymar influenced his decision to sign for Atleti instead.
He told L'Equipe: "It was above all a sporting choice. I knew that if I went to Barca, I would have found myself as the fourth attacker.
"My game time would have reduced I think. In fact there was more chance of me staying at Sevilla than going to Barcelona."
Gameiro is also looking forward to working with Simeone, adding: "He told me that he was looking for a player like me who was able to provide an effort in defence like in attack.
"And also to be a goal scorer. Simeone wanted above all someone who could blend into the collective."