Simeone spoke to DAZN before the 1-0 victory over Girona, in which Griezmann assisted the only goal before being given a ceremonial send-off on the pitch.
"For the history of Atletico, Griezmann is possibly the best we have had here. He is an extraordinary boy and a genius. Among all those I have managed here, he is a genius. He is the most decisive."
Simeone addressed the difficulty of watching close associates from the defining era of his tenure depart one by one.
"These are uncomfortable conversations, but they have to be had. I always thought I would leave the way I arrived, believing that whatever I decide will be best for Atletico. That is why we talk to Griezmann, to Savić, to Godín — to all the players who are leaving us, who were so important in this process."
He was direct about his own future when asked whether Sunday's emotion might prompt him to reconsider his position.
"I think about myself, about how I am and how I face a new season. With the excitement that good players might join. This is about players, not managers."
On the race for third place in La Liga heading into the final round of fixtures, Simeone kept the focus on effort rather than the table.
"We only want to play a good match. Villarreal has a difficult game and then finish the season in the best possible way having left everything we have — I guarantee that."
Simeone took charge of Atletico Madrid in January 2012 and has since won two La Liga titles, two Europa Leagues, two UEFA Super Cups and a Copa del Rey. His tenure shows no sign of ending — but the squad he built around Griezmann is being dismantled around him, piece by piece.