The 19-year-old forward has emerged as one of the most sought-after talents in European football.
Felix’s current contract does include a €120 million (£103m/$136m) release clause, which could prove a sticking point to some in the pursuit of a player with limited experience, but it is considered to be only a matter of time before a big-money move is made.
Costa admits that it will become impossible for Benfica to retain the services of a player with such potential, telling Tuttosport: “Someone called him my heir. Or the new Kaka. The truth is that Felix is only Felix.
“He has an extraordinary sense of play and he has a rare ability, he can guess what will happen in front of the goal. He is a modern number 10, a second striker with a remarkable sense of goal, he scored 10 goals in the league.
“€120m release clause? We will try to keep him as long as possible, this applies to Felix as it does to all the others.
“This is the club's policy, then we will see why we are aware that the clauses exist and that certain players cannot be held back indefinitely in Portugal.”
Another of those to be generating transfer talk at Benfica is highly-rated centre-half Ruben Dias.
The 21-year-old is already a senior international with Portugal and, like Felix, is said to be attracting admiring glances from Juventus and Manchester United as both sides seek long-term solutions to questions at the heart of their respective defensive units.
Costa added on Dias: “If he will go away I don't know. We would like to keep him still and Ruben knows that here he would have a lot of attention.
“The club needs to sell to make cash. We will see how the summer market will develop.”