The Argentine centre-back says the squad are united behind the coach of Los Cochoneros despite the weekend setback at the hands of title rivals Barcelona
Sunday's 4-1 defeat by Barcelona harmed the title chances of the club from the capital, and although a nine-point gap has opened up at the top of La Liga, the summer signing from Getafe claims that his compatriot has the full backing of the dressing room.
“I do not think his renewal is in question [because] the team is well and the players believe in the project,” the 33-year-old said at a press conference.
Atletico have not won La Liga since 1996 but Simeone's side impressed in winning the European Super Cup in August and the Europa League in May.
And Diaz believes the silverware the trainer has already delivered, combined with the resolve the 42-year-old has instilled in the players, dictate his methods should not be questioned.
“I think Simeone has [already] proved his worth with titles,” Diaz said.
“He changed the mentality of all the players and it shows on the field and in the locker room."
Atleti's next test sees them host Celta Vigo this Friday.