Griezmann is expected to leave Barcelona this summer and was jeered by home fans on Sunday.
"The support for him was enormous, we love him very much and we know that if he continues here we will continue to be more competitive," Simeone said.
"There is always criticism and there will be criticism."
A second-placed finish and a Europa League title clearly pleased the coach.
"We always think positive, to be optimistic about everything," he added.
"We ended a wonderful season with a lot of difficulties, but we finished second... that generates growth, enthusiasm and desire to keep competing."