The Rojiblancos coach is thrilled with the club's signings this summer but has not ruled out further purchases despite their Supercopa win over Real Madrid
The Rojiblancos have signed a host of players over the past few months, including Mario Mandzukic from Bayern Munich, after losing some of their key components - namely Diego Cost - from their La Liga title-winning squad of last season.
Mandzukic got his Atleti career off to a perfect start when he scored in his side's second-leg Supercopa de Espana clash against rivals Real Madrid at the Vicente Calderon on Friday – a goal that clinched the trophy for Simeone's men.
And following his important strike against the European champions, Simeone was delighted with the impact of Mandzukic and fellow new arrivals Antoine Griezmann and Guilherme Siqueira.
"The new players give me other benefits. They are improving. I have seen an important match of Mandzukic, Griezmann gave us an improvement in the second half, Siqueira had a great game," Simeone said.
"The squad is not closed. Anything can happen.
"There have been at least four changes because Mandzukic is not [Diego] Costa, Griezmann is not [David] Villa, Siqueira is not Filipe [Luis] and we'll see how the team grows without losing the essence."
The Supercopa de Espana win over Real helped, in part, banish the memories of May when Atletico lost the Champions League final to their fierce rivals.
However, Simeone admits that, while his team's latest triumph cannot completely erase the disappointment of losing in Lisbon, the victory has given satisfaction to the Atleti players.
"It's not the same as the Champions League. We live today's game," he said.
"The other time it did not work out, but we are always competitive and that makes us very proud."
Simeone’s men kick off their title defence when they play their first game of the new Primera Liga season away to Rayo Vallecano on Monday.