The Belgium international is being integrated into Diego Simeone's side after joining on a free transfer from Borussia Dortmund at the start of this month.
Witsel spent the last four seasons with Dortmund, having joined from Chinese Super League side Tianjin Quanjian in the summer of 2018.
He won the DFB-Pokal with Dortmund in the 2020/2021 season and German Super Cup in 2019 and counts Standard Liege, Benfica and Zenit Saint Petersburg among his former clubs.
Witsel will compete for a place in midfield with the likes of Saul Niguez, who has returned from a season-long loan at Chelsea, Geoffrey Kondogbia and Daniel Wass, while Joao Felix, Antoine Griezmann and company are upfront, with highly rated goalkeeper Jan Oblak leading from the back.
Witsel believes Atletico can compete with the quality in the side and improve upon last seaaon's third place finish.
"This is a group with a lot of quality," Witsel said at his presentation at the Wanda Metropolitano.
"I could say many players – Koke, Joao [Felix], [Antoine] Griezmann, Yannick [Carrasco], [Matheus] Cunha.
"We have a group with a lot of quality and it is very important because there is a very good mentality, with players who always want to work hard.
"I've been through many clubs and it's true that the fact of being here and having trained with the group, I think it's the group with the highest quality of all my career. There are a lot of internationals, I'm very proud to be here and to be part of this group."
Witsel added on his new boss Simeone: "It is clear, he is one of the best coaches in the world, it is one of the reasons why I am here."
"In recent days we have focused on the physical and I have not been able to talk much with him, but I am very proud to work with him.
"It doesn't matter how old you are, at 33 or 23 you can always learn something, and you can always learn from him.
"I was free and I chose Atletico because I wanted to continue at a high level, I know I don't have ten years left, but I want to take advantage of my last few years to play at the highest level, Atletico is at that level and that's why I'm here."