Lennox Lewis has warned David Haye he must knock out Wladimir Klitschko because there is "no way" the judges will award him a points win in Germany.
Haye, 30, faces Klitschko in a world title decider on Saturday with Lewis wary of Germany's reputation for questionable judging decisions.
Ukrainian-born Klitschko has been based in Germany for several years.
"He's got to knock him out. When you go into the other guy's backyard you can't hope to win on points," said Lewis.
Britain's Haye bids to unify three of the four world heavyweight titles when he puts his WBA crown on the line and tries to snatch Klitschko's IBF and WBO belts in Hamburg.
Lewis, Britain's former undisputed heavyweight king, was ringside in Cologne last Saturday to watch Birmingham's Matthew Macklin lose his WBA middleweight title challenge in a highly controversial split decision.
"I don't see Haye winning on points. There is no way. It's such a big uphill battle," admitted Lewis.
"I commentated on Matthew Macklin against Felix Sturm in Cologne and it was disgraceful. It was so bad.
"As soon as that happened I thought about David and said 'dude, you're coming over to fight in the other guy's backyard? They're not going to give it to you.
"They are not going to be nice to you. Don't think you're going to get a fair shake. You know what you're going to have to go on there and do. Simple as that. Bring your own judges - your fists'."
Haye was, however, awarded a points decision against Russian Nikolay Valuev to win the WBA title in Germany in November 2009.
Meanwhile, Haye says he is confident he will fight Vitali Klitschko before his retirement in October.
Vitali, 39, is scheduled to defend his WBC belt against Tomasz Adamek in September but Haye is confident the Ukrainian will find a way to face him instead.
"I think after the fight things will change pretty quickly, I'm positive about that," said Haye.