Griezmann scored his 15th LaLiga goal of the season during Atletico's 3-2 victory over Valencia on Wednesday.
The France international has continually been linked with a move to Barcelona, who are nine points clear at the top with four games remaining.
3 - @atletienglish's @AntoGriezmann is one of the three players to have scored 15+ goals in LaLiga in each of the last five seasons, alongside Lionel Messi and Luis Suarez. Prince. pic.twitter.com/CGd7wk78dZ— OptaJose (@OptaJose) April 24, 2019
But Simeone said Griezmann, who is contracted until 2023, was still shaping as a vital part of his Atletico squad for next season.
"A very important player for the present and the future of the club and the team," he said, via Mundo Deportivo.
"He is one of the captains and we hope that next season he will have an intense season like now."
Angel Correa's 81st-minute goal proved to be the winner for Atletico, while Valencia were left in fifth – two points behind Getafe and having played one more game.
Griezmann said his side wanted to finish as close to Barca as possible as Ernesto Valverde's men close in on the title.
"We have games left," he told beIN SPORTS. "We will see [when] they do it. If you cannot be first, then second.
"We want to be as close as possible so that one day we will be first."
Valencia boss Marcelino remains hopeful about his side's chances of a top-four finish, with matches against Eibar, Huesca, Deportivo Alaves and Real Valladolid left in their league campaign.
"We know we have more games. I don't trust the calendar. The last defeat was against Rayo [Vallecano], which should make us think that any game is decided by details," he said.
"It will [not] be decided until the end. We play at home on Sunday and we have to win.
"It is a very important game and the effort is accumulated, the options for fourth place are intact."