The quartet were the Reds’ last participants at the World Cup, with Lovren playing in Croatia's defeat in Sunday’s final after Henderson and Alexander-Arnold’s England had lost to Mignolet’s Belgium in the third-place play-off on Saturday.
All four will now take a near-three-week break and are set to return to their club seven days before Liverpool host West Ham United in their opening game of the 2018-19 Premier League campaign.
Klopp said: “They are back as well at August 5, I think, then we have proper week to prepare the season.”
The boss has already confirmed that new signing Xherdan Shaqiri will be involved in the Reds' tour of the USA, with Roberto Firmino to report to the subsequent pre-season training camp in France.