Hall of Famer Johnny Lewis, who is regarded as Australia's most successful boxing trainer is practically pleading with WBO welterweight champion Jeff Horn to forget about a mandatory fight with Terence Crawford next April in Las Vegas.

Lewis, who guided Jeff Fenech , Kostya Tszyu and many others to multiple world championships, would rather see Horn move up to junior middleweight to take on Anthony Mundine in what would be a major fight in Australia.

Lewis believes Horn is struggling to make the weight limit of 147 and he doesn't want to see a "weight drained" version of the boxer enter the ring against Crawford.

Last week, Horn stopped Englishman Gary Corcoran in 11 rounds in Brisbane .

The boxer reportedly had to cut between eight to nine pounds in a 24 hour period before the weigh-in - and it's no secret that Horn has physically fought to get down to the welterweight limit in his last few fights.

“Jeff Horn looked so drained at the weigh-in for the Corcoran fight it was like he’d had a bout with Count Dracula the night before,’’ said Lewis to Courier Mail.

“He looked emaciated. Jeff Horn has been the best thing to happen to Australian sport in a long time and I would hate to see him fight Crawford seriously disadvantaged. Jeff relies so much on his huge mental strength to keep pushing through. I’m not saying he can’t beat Crawford but it’s madness to give him such a huge headstart.’’

Lewis believes the safe bet, is to move up to 154 and get a big payday against Mundine. The veteran coach says a fight between Horn and Mundine would "capture the imagination" in Australia.

"[Struggling to make weight], it catches up with you,’’ Lewis said. “Gary Corcoran was hitting Jeff with a lot of lead right hands the other night that shouldn’t have been landing.

“If I was advising Jeff I’d say forget what Crawford or his promoter Bob Arum want, you cut the best deal you can and fight Mundine and then suit yourself after that.

“If you’re having trouble at welterweight, move up to junior-middleweight because there’s probably even more money for you up there.’’