Anthony Joshua's coach says the British heavyweight was struggling with a virus when he defeated Dominic Breazeale inside seven rounds as he retained his IBF crown.

Kiwi boxer Joseph Parker is the mandatory challenger for Joshua's title, with negotiations for that bout scheduled for November. Joshua beat American fighter Breazeale in London last weekend, while Parker prepares to fight Solomon Haumono in Christchurch on July 21.

And the Brit's coach, Rob McCracken, has revealed that Joshua was far from 100 per cent as he fought Breazeale, before he knocked the American to the floor twice in the seventh round.

"He had a virus in that contest. He wasn't feeling great," McCracken told the Daily Mirror.

"There has been a bug going round and Big Josh had it - but he kept it under the radar. He won't say it because of the way he is, but he wasn't 100 per cent."

McCracken has coached Joshua since he won gold at the London Olympics in 2012.

He is coach of the British boxers heading to the Rio Olympics next month and he's worked with Joshua since he turned professional.

"He wasn't ill, but he certainly wasn't 100 percent, yet he still wanted to go through with it," added McCracken.

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"Breazeale is big and very physically strong, but Anthony stood behind his jab, took his time and showed he's ­developing and learning. He's great for British boxing and has huge ­experience of staying calm under pressure now.

"He has dealt with the media, he has dealt with 22,000 people screaming, he is well versed in dealing with pressure, ­although people don't think he is, and he didn't get flustered.

"With the exception of Lennox Lewis you can go back forever looking for a similar British heavyweight.

"Anthony Joshua looks the part, he's a good role model."

Joshua has won all 17 of his professional fights by knockout, with only two going past three rounds.