But Joshua has hit back, telling Sky Sports: "Lennox is a clown. I don't respect Lennox.
"Me and Lennox are not the same. My legacy is to sit back and enjoy the younger generation coming up, and not to be involved. Just to appreciate what it takes to get there.
"Lennox isn't like that."
However, Lewis has hit back, saying that Joshua's words are merely part of an agenda on the part of his manager, Eddie Hearn and that his only criticism of Joshua was the protracted negotiations about a fight with WBC champions Deontay Wilder.
Joshua is set to fight Ruiz Jr again in December but the venue - Saudi Arabia - has made the fight controversial.