Oblak, 25, has gone from strength to strength since joining Atletico from Benfica in the summer of 2014, and has kept 28 clean sheets in 47 appearances for his Spanish club this term.
A number of teams - including Liverpool and Arsenal - are believed to be interested in the Slovenian, but Simeone is determined to keep the stopper at the Wanda Metropolitano.
"Happy to have him with us. He found it hard to get into the team at the start but was patient and is now among the best goalkeepers in the world. I hope we have him with us [next season] and he is happy to be here," Simeone told reporters.
Atletico will face Marseille in the Europa League final on Wednesday night.