Felix scored one and set up the other as Atletico completed a perfect pre-season with a 2-1 International Champions Cup victory over Juve in Stockholm.
Simeone has been impressed with what he has seen from Felix, who netted 20 times in 42 games in all competitions for Benfica last season.
"Joao has many capabilities. He is adapting very quickly to what the team needs," the Atletico coach told a news conference.
"He has a vision that allows him to adapt to many positions and is in a process of adaptation and the best thing he has is that, I said from the first day, his desire to learn.
"He wants to learn and with that the adaptation process will be shorter. Talent is innate, but the desire to learn is the shortest path that a player has to perform."
Atletico have gone through a rebuild in the close season, the likes of Felix, Marcos Llorente and Kieran Trippier joining, while Antoine Griezmann, Rodri, Lucas Hernandez, Diego Godin, Juanfran and Filipe Luis are among those to have left.
"We are open to everything that can happen, transfer wise. There is nothing that can surprise us because obviously there is always something happening until the end so we have to be prepared for that," he said.
"Angel Correa is training in an extraordinary way since he arrived back and there's not any situation that leads me to think about him leaving the team."
Correa had a difficult season in front of goal in 2018-19, scoring just five goals in all competitions and three goals in 36 games in La Liga.
Atletico begin their La Liga campaign at home against Getafe on August 18.