Liverpool must seal the signing of Bayern Munich midfielder Thiago Alcantara if they want to avoid a "drop-off" next season, says Gary Neville.
The 29-year-old, who played an instrumental part in the Bavarian outfit's Treble-winning campaign, is set to leave the Allianz Arena after seven years in Germany.
It is understood the Premier League champions, who finished 18 points clear of Manchester City, have reservations about paying over £20m for a player who only has one year left on his contract.
While Chelsea have strengthened their squad with six new signings ahead of the new season, spending in excess of £220m, Liverpool have only signed left-back Kostas Tsimikas from Olympiacos.
Manchester United have also brought in Ajax star Donny van de Beek, while Arsenal's capture of Brazilian duo Willian and Gabriel Magalhaes suggests they could improve under Mikel Arteta next season.
And Neville has warned that without adding a playmaker such as Thiago to their ranks, the Merseyside club risk experiencing a "slight drop-off" against their rivals during the 2020-21 campaign.
“To get to a Champions League final, win it the following season, and then to go again to win the Premier League title is a huge emotional drain on that group of Liverpool players for three years,” Neville told Sky Sports.
“To ask them to go again and achieve that same standard would be a superhuman effort.
“It wouldn’t be ridiculous to suggest there will be a slight drop-off, if they don’t somehow stimulate that squad by doing something to give them that lift again.
In Pictures | Liverpool's first Nike kit for 2020-21 season
"Thiago would be the big one. He is world-class and would give them a world-class presence in an area of the field where they don’t have one.”
Klopp's side begin their title defence with a home fixture against newly-promoted Leeds United to Anfield on September 12.
