Lennox Lewis' former trainer Harold Knight has warned Deontay Wilder he risks putting his 'legacy on the line' against Tyson Fury.
The former WBC heavyweight champion will fight a trilogy bout against the Briton at the T-Mobile Arena in Las Vegas on October 9.
With the former champ apparently changing things up including bringing in a new coach Malik Scott to replace the outgoing Mark Breland, Knight believes another defeat for Wilder is unthinkable.
And Knight - who has worked with the likes of Lewis, Scott and Dillian Whyte - advised his former pupil to tell him the truth no matter what.
He told MyBettingSites: "From experience and being around Malik for a long time, it's a fine line between friendship and business.
"So if Malik can keep it business rather than friendship with Wilder, I believe they can do some good things.
"This is business, this is high stakes boxing, this is world championship boxing, legacy is on the line.
"If you are a friend of the guy you train, you are going to tell him what he wants to hear instead of what he needs to hear.
"It does not work like that, not in championship boxing, especially coming off a loss and going into a third fight.
"You want to be going in training camp and say: 'I like you and respect you but I'm not going to tell you what you want to hear'.
"This is what I hope Malik has done. Generally you want to eliminate fanboys, you want to have people around you that are going to take you to another level."
Wilder recently revealed he hired Scott for his 'genius' earlier this year - despite knocking him out in 2014.
Scott, also a former sparring partner of The Bronze Bomber's, will act as his chief second for the trilogy fight with The Gypsy King this weekend.
But Knight, who trained Lewis out of the Kronk Gym in Detroit, has doubts about his ability to give him the right instructions on the night.
"Malik hasn't been in the corner before as head trainer, but you have to start somewhere," he added.
"So once again, when you get to this world championship level, legacy on the line, how you react in the corner is important: what you tell your guy when he's losing or winning, or what you tell him to help get him through.
"If you lose this you're done, so you want to be able to pull out all the stops in this fight."