Benfica released a statement on Wednesday confirming that the Spanish side made an offer that exceeded the 19-year-old attacker's €120m release clause.
However, they have no obligation to accept the bid because Atletico want to pay it in instalments to soften the blow such an investment will have on their financial health.
Although Benfica are still considering the deal and have not announced a decision, Felix is expected to be unveiled as an Atletico player in the near future.
As well as the €17.5m he stands to make over the duration of his contract at the Wanda Metropolitano, Goal can reveal that Atletico have slapped a €250m (£225m/$315m) release clause into the deal - a higher fee than any of his future team-mates have in their contracts.
Felix will become the most expensive signing in Atletico's history if Benfica give him the all clear to move this summer.
He will then team up with the Rojiblancos on July 4, just three days before they begin their pre-season preparations.
Felix joined Benfica's youth system from Porto in 2015 and broke into the first-team in 2018-19.
He went on to make 43 appearances in all competitions, scoring 15 times in 26 league games as Benfica claimed the Primeira Liga crown.
He also had a hand in Portugal's UEFA Nations League victory this year, playing 70 minutes as they beat Switzerland in the semi-final, though he was an unused substitute in the 1-0 win over Netherlands in the final.
Atletico, who finished second in La Liga last season, have seen several players come and go in the current transfer window.
While veteran defenders Diego Godin and Juanfran were released after their contracts expired, Diego Simeone's team have also waved goodbye to Lucas Hernandez, who joined Bayern Munich, and Luciano Vietto, sold to Sporting after his loan spell at Fulham ended.
Antoine Griezmann and Rodri are also expected to depart while Felipe Luis, who is out of contract on June 30, is yet to agree to fresh terms.
Meanwhile, they have signed Marcos Llorente from city rivals Real Madrid and centre-back Felipe has joined from Porto.