The Cat, 38, defeated Daniel Dubois, 28, and took his IBF title in July to become the undisputed heavyweight champion of the world, but Lewis believes Usyk should quit while he is ahead and throw in the towel.
Speaking with Sky Sports, the 60-year-old former heavyweight champion said: “When a guy retires, it's really down to him.
“He's got to feel that push that he wants to retire, but he can teach a lot of young boxers a lot of different things: dedication, hard work, sacrifice, because he's been through that.
“So I would say to him to retire at your own time, but retire on top. Like I did.”
Lewis praised Usyk for moving up from the cruiserweight division - of which he was the undisputed champion - to the heavyweight, where he claimed victims like Dubois, Tyson Fury, 37, and Anthony Joshua, 35.
Lewis also admitted The Cat would have given him trouble during his hayday.
He said: “I think he would have fared really good because he's doing something Evander Holyfield did [move up from cruiser successfully].
“In this era he's beaten all the big guys and all the guys that were in front of him. So he's done a great job.”
Lewis said he understood the difficulty of becoming an undisputed champion, calling it “the hardest thing to do”.
He explained: “It's definitely the hardest thing to do because you basically want to be the best in boxing and take all the belts for yourself and be the number one guy.
“There's always other boxers out there that don't want you to achieve that. They're standing by, they want to be beat you, they want to be the first boxer to beat you. That's why you've got to make sure that you retire on top.”
Usyk will next face either Joseph Parker, 33, or Fabio Wardley, 30 after the WBO ordered the winner of the fight - which will take place in London’s O2 Arena on October 25 - to be the mandatory challenger to his heavyweight championship.
The Barista recently said the chance to fight Usyk for the heavyweight title was a “huge motivator”, but was focused on defeating Lupesoliai La’auliolemalietoa first.
He said: “That's a huge motivator. I'm trying to not get too distracted by that.
“Obviously that is the dream, that is everything - to fight for a world title. So we've got to tick off October 25 first and get that out the way. But then it's seriously on to the big leagues.”
