Lennox Lewis has warned David Haye he must knock Wladimir Klitschko out on Saturday because there is "no way" the judges will award him a points win in Germany.

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.

However, Germany has a reputation for questionable judging decisions and fellow Briton Lewis was ringside in Cologne last Saturday to watch Birmingham's Matthew Macklin lose his WBA middleweight title challenge in a highly controversial split decision.

Haye has vowed to knock Klitschko out rather than let the fight go 12 rounds anyway and former undisputed champion Lewis - who was denied victory in a controversial draw in New York in his first fight against Evander Holyfield in 1999 - says he has no other option.

"He's got to knock him out," Lewis said.

"When you go into the other guy's backyard you cannot hope to win on points.

"I saw that myself against Evander Holyfield. I beat him but after the fight people were saying 'why didn't you knock him out?' and I was saying 'dude, did enough, I didn't have to knock him out!'.

"I don't see him winning on points. There is no way. It's such a big uphill battle.

"I commentated on Matthew Macklin against Felix Sturm in Cologne and it was disgraceful. It was so bad.

"Sturm's demeanour was like he was saying to Macklin 'what are you doing, you're not going to win anyway!'.

"I don't know how you could give Felix Sturm eight rounds. I'm watching the fight and Macklin's punch count is triple Sturm's in every round. Yet they didn't give it to him.

"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!'

"He has the talent to do it.

"He has to use his speed. If David is 100 per cent he should win."

Haye was supposed to fight Klitschko in 2009 but had to pull out through injury.

The intervening two years have been dominated by on-off negotiations and tiresome trash-talking but Lewis, who will be part of the Sky Box Office broadcast team, believes the protracted saga has boosted interest in the fight.

"It's a big fight because nobody knew if it was going to be made or not," he said.

"It was supposed to happen and then didn't. It's going to happen this time.

"Me and Mike Tyson were like that for years, because he was incarcerated for a while plus during that time people were wondering if he'd fight when he got out. There was actually a lot more time between me and Tyson than this particular fight."

Haye claims to be the saviour of a dull heavyweight division but Lewis believes he has yet to really make a splash outside Europe.

"To a certain degree he has worldwide support, but they haven't seen enough of him to support him 100 per cent.

"He absolutely needs this fight to establish his legacy. What will they say after the fight? If he loses they will say 'he's had one crack at it and he's failed'."