The Atletico Madrid forward is set for Stamford Bridge again, after a previous loan spell at the club.
While Felix is coming into the squad, the Blues are losing homegrown midfielder Conor Gallagher to Atleti.
Maresca stated on Felix: "First of all because he's a good player. He's a talent, the club already know him from two years ago.
“I think the good thing about Joao is he can play in different positions with us. He can play inside, he can play as a No.9, he can play outside."
He then added if the fans will understand the sale of Gallagher:"(Laughs) This question is for the fans. I don't know to be honest.
“The only thing I can say is that it's not from today. It's already been days, weeks that the agreement is there. It's already been there for days and weeks. It's nothing new."