Felix, who signed for a club-record fee of about 120 million euros ($140.46 million) from Benfica last year, was impressive in Atleti’s 6-1 home demolition of Granada in their Liga opener.
However, he received some media criticism for his anonymous display in the 0-0 draw at Huesca last weekend.
“Last pre-season he showed the same desire and happiness in his game as he’s showing right now,” Simeone told a news conference ahead of Saturday’s visit of Villarreal.
“Until he got injured he started last season really well, and hopefully he can continue as he is and carry on growing with the team. We want to make use and take advantage of a footballer who we really believe in.”
The Argentine coach refused to be drawn on Spain manager Luis Enrique’s decision not to select any of his players for international duty, and also played down the likelihood of new signing Luis Suarez being paired up front with Diego Costa.
“I spoke to Costa before the season started and he knows what I want from him, what I need and what we have in mind.
“Luis joined only recently and we can’t wait to see what he brings us. We’ll follow the path I’ve discussed with those players individually.”
Atletico are likely to be without defender Jose Maria Gimenez, who tested positive for COVID-19 last month.
Villarreal could have up to seven injury-enforced absentees, including new arrivals Pervis Estupinan and Francis Coquelin.