Hazard, who suffered through a disappointing campaign with Chelsea in the Premier League, is one of the key men for a Belgium side that is considered by many as one of the favorites in Russia.
The 27-year-old was a slight injury worry, having limped out of 4-1 friendly win over Costa Rica after suffering a kick on the leg, but Belgium have calmed fears of him missing out and Courtois expects him to be key to their performance.
"It's not only Eden at his best, and I don't think I've ever seen him train and play this amazingly," Courtois told reporters.
"He's reached another level of his game and I hope he can show that.
"But we also need Romelu [Lukaku] to score goals, I need to play well, we kneed [Kevin De Bruyne] at the level he's at at City.
"We need our best players at their best and everyone is training well at this moment."
Despite a lacklustre showing in league play for Chelsea, Antonio Conte's side closed the club season with a win over Manchester United in the FA Cup final, and Belgium boss Roberto Martinez thinks the trophy to close the year was just the boost his star winger needed heading into Russia.
"I think Eden ended the season with winning a trophy, with his performances in the final and semi, have prepared him well for the World Cup," the former Swansea boss said.
"He's in good form, looks fresh and ready. The players we have around help him too. In the last two friendlies, he's looked very sharp."