And Jurgen Klopp's side have only improved this season, as Liverpool have amassed a series of records while surging to the top of the Premier League.
As things stand, Liverpool sit 22 points clear atop the Premier League, having dropped just two of the 75 points available to them this season.
The Champions League, though, has been a bit different, as Liverpool did lose 2-0 to Napoli in their opener before drawing the Italian side in their penultimate game of the group stage.
But Felix knows that Atletico Madrid face a major challenge when the Spanish side takes on last year's winners in the round of 16.
"It will be a very difficult tie", Felix told Eleven Sports.
“Perhaps of all the teams, they are the most difficult team.
“Liverpool are in good shape, in excellent form, they are the defending champions and it will be very difficult, as with any match in the Champions League.
“But against this Liverpool who are doing very well, it will be even more difficult."
Felix, playing in his first season for the club, has scored four goals in 23 games across all competitions.
Atletico Madrid are set to face Granada and Valencia in the run up to that round of 16 match on February 18 while are set to visit Norwich on February 15 following their winter break.