The €120m signing has struggled to get off the bench for Atleti this term.
He told the Athletic: "Here I have learned some things that are difficult to learn elsewhere. The way we defend. I think I have improved a lot in that. Also when it comes to turning with the ball and going on the run. It is the most important."
On his difficulties this season, Felix continued: "I don't know. There are a lot of reasons, I can't say one.
"We know what's going on, but I'd rather not talk about it."
Atleti will meet Manchester United in the Champions League round of 16, he added: "It's great to play against friends. I exchanged messages with Bruno when the draw was made (...). Cristiano is an example for all of us in the national team, he doesn't give much bad advice and we like to listen to him."
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