Endo was recruited as part of a midfield overhaul last summer, arriving in the same window as Alexis Mac Allister, Dominik Szoboszlai and Ryan Gravenberch.
The Japan international went on to make 43 appearances during his first season at Anfield, chipping in with two goals and an assist.
Despite proving to be a useful squad player, there has been a suggestion that Endo could leave Liverpool after just one full season.
Slot rules out Endo sale
Liverpool reportedly rejected bids from Marseille for Endo earlier this summer, indicating that they are still keen to retain the 31-year-old's services.
Slot has now confirmed that he wants to keep Endo, insisting the midfielder still has a role to play at Anfield this season.
"It is not always about the player himself, it's also about the competition he faces," Slot told reporters after Sunday's win over Brentford.
"We have many good midfielders like we have many good players. We are really pleased with the way Wata is training for us but he has some good competition and I think you saw today a good performance from all three midfielders, so it is not always about him - it is also about the others.
"He will be important for us during the season because we need all of them; we all know how long a season can be over here and how many players you need - and he is one of them that we are going to need in the upcoming season."
What will Endo's role be this season?
Although Slot is keen to retain Endo's services, the midfielder is not a guaranteed starter and will have to settle for a squad role.
Endo was an unused substitute for the league opener against Ipswich, before he featured a stoppage-time substitute in Sunday's fixture.
However, Slot has suggested that a long and demanding season will test Liverpool's squad depth, ensuring Endo will still have a role to play at Anfield this term.
After kicking off the campaign with consecutive 2-0 wins, Liverpool will attempt to make it three wins in three matches when they face rivals Manchester United on Sunday.