The Eagles won the race to sign the 21-year-old from River Plate in the summer, and he immediately earned plaudits with his performances domestically and in the Champions League.
Fernandez has struck three goals and five assists in 24 appearances for Benfica during his debut season so far, and his form earned him a spot in Argentina's 2022 World Cup squad.
The midfielder quickly forced his way into Lionel Scaloni's first XI in Qatar and registered one goal and one assist in seven appearances to help his country win their third World Cup title.
Fernandez was bestowed with the Best Young Player award after playing a key role in Argentina's run to the trophy, and Benfica have a fight on their hands to retain his services in January.
The likes of Liverpool, Manchester United, Real Madrid and Chelsea are said to be keeping an eye on Fernandez, and the latter are reportedly willing to pay as much as £105m to beat their rivals to his signature.
Chelsea have seemingly been handed a boost in their pursuit of Fernandez, with Benfica president Costa confirming that a figure around that area would be deemed acceptable in the winter window.
"We will sell Enzo Fernandez in January only for the €120m (£106.2m) clause. We would not like to sell Enzo Fernandez in January, but we are willing to satisfy the boy in the event of an offer of €120m," talkSPORT quotes Costa as saying.
Benfica are under no pressure to accept a low offer for Fernandez in January, as the 21-year-old remains under contract with the Eagles until the summer of 2027.
Eagles manager Roger Schmidt has confirmed that he has held discussions with Fernandez over his future, and he will respect whatever decision the player makes over the coming weeks.
"I can't reveal those conversations. When I talk to the players, these are things I keep to myself. What I can say is what I've already said. We all know what football is like," Schmidt added.
"These young people have opportunities, and it's not just about Enzo. If they have opportunities, they have to make decisions, and I respect them.
"I can advise them, but they only have one career. If I can convince them or influence them in a certain way, I try to do it, but I accept their decisions."
Benfica have not lost a single competitive game since Fernandez's arrival, winning 12 and drawing one of their opening 13 Primeira Liga matches to storm to the top of the table.
Schmidt's side also beat Paris Saint-Germain and Juventus to top spot in Champions League Group H and will take on Club Brugge in the last 16.