After losing captain Ivan Rakitic and Alberto Moreno to Barcelona and Liverpool respectively, Sevilla are surprisingly among three teams level on 13 points at the top of La Liga.
Defending champions Atletico - also unbeaten - are two points further back in fifth position.
And prior to this weekend's meeting at the Vicente Calderon, Simeone is wary of Sevilla under Unai Emery.
"We are facing a very good team [Sevilla], which has signed very talented players," said Simeone.
"I already told you in Cadiz [the sides played against each other in pre-season] that they have a competent squad with many important players in different lines.
"Those things make Sevilla a very competitive side as they have been. Emery's work is really good as he usually does in those teams where they let him work.
"It's going to be a massive match between two teams, which I think have many similarities."
Simeone also insisted that France forward Antoine Griezmann is a key player for Atletico following his close-season arrival from Real Sociedad.
Griezmann scored 16 league goals for Sociedad last term, although he is yet to find the net for Atletico in Spain's top flight in 2014-15.
Simeone, however, thinks the 23-year-old is still adjusting to life in Madrid.
"Griezmann is a very important player for us. We need him in his best shape," he added.
"I think players are important when they reach some steps playing continuously. He is a player who is able to score, able to go deep with the team.
"He is a player we need in his best form and he is in that step as he is very young. It's not the same, with all the respect to Real Sociedad, playing for them or playing for Atletico Madrid.
"It's a different point of view and he is in that period of showing the best things he has."
