The 25-year-old returned to the Premier League by joining Liverpool in July and is the competition's top scorer with nine goals in 12 games.
"He's a top, top, top player. He did not get his chance at Chelsea – maybe because of the manager, because of the other players? I don't know," Hazard told reporters.
"He has quality but in that period I remember we had me, Willian, Oscar, so for him it was not easy.
"He is a fantastic striker and this season he has scored a lot of goals. It is always good to play against a friend but Liverpool is not only about Salah. They have a lot of quality players."
Champions Chelsea will travel to Anfield on Saturday, with Antonio Conte's men three points ahead of their rivals.
Chelsea have little time to prepare for the trip after beating Qarabag 4-0 in Azerbaijan in the Champions League on Wednesday but Hazard said they would be ready.
"A lot of players didn't play on Wednesday and I played only 60 minutes and N'Golo (Kante) also came off, so we can be fresh on Saturday, even if the game is close," the 26-year-old added.
(Reporting by Aditi Prakash in Bengaluru; Editing by Peter Rutherford)
