Anthony Joshua suffered a devastating seventh-round knockout loss to Ruiz Jr at Madison Square Garden in New York early on Sunday morning.
The Olympic gold medallist was dropped a staggering four times before referee Mike Griffin waved off the contest, an act which saw Joshua lose the WBA (Super), WBO, IBF and IBO heavyweight titles.
The post-mortem of Joshua’s first career loss has raised plenty of questions, with many wondering if he was in the right frame of mind in the build-up to his American debut.
As is often the case when a fighter loses, the game plan Team Joshua implanted for the stocky Ruiz was dissected and criticised.
Lewis is amongst those who have been critical of Joshua’s approach for the fight and believes he needs to dump McCracken, as he did when he lost the WBC title to Oliver McCall at Wembley in 1994.
“I say you can’t go to university with your third-grade teacher,” said the former undisputed heavyweight king and British boxing legend said.
“They won’t have the answers you need at that level. You need a professor by then.
“McCracken is A1 without question but maybe not the fit for the style ‘AJ’ needs to fight.
“I switched to Manny Steward who understood how to leverage all of my physical attributes and skills and showed me everything I needed to know for success.
“Aside from that ‘AJ’ was not prepared for anything Ruiz brought to table.”
Rumours have been floating that Joshua was badly hurt in sparring ahead of the bout and that his father Robert wanted the contest to be scrapped.
Joshua’s promoter Eddie Hearn has emphatically dismissed that notion and is adamant the Watford native was in good shape going into the fight.
He told the Daily Telegraph: “Absolutely there is no truth that he was badly hurt in sparring, there were no health concerns going into the fight.
“The biggest concern was a stye on his eye.
“He’s putting on a brave face after the defeat, but he is already starting to think about getting revenge.
“The rematch is a huge fight and there’s a lot of pressure on AJ to win it.”