Joseph Parker's first defence of the WBO world heavyweight title will be against unheralded Romanian Razvan Cojanu, who has taken up the fight at late notice.

With mandatory challenger Hughie Fury having this week pulled out of the fight citing a back injury, Parker's management sought a swift replacement for the promotion in Auckland on May 6.

They have revealed Parker will face the lanky Cojanu, 30, who has won 16 of his 18 fights, including nine by knockout, and is ranked 14th by the WBO.

The holder of the WBO Asian Pacific title, Cojanu represents a significant step down in class from the unbeaten Fury, who was the No.1 ranked challenger in the division.

Following an accomplished amateur career, 2.02m-tall Cojanu made his professional debut in 2011, recording an immediate loss to Mexican Alvaro Morales.

The other defeat came two years ago when he was knocked out by middling American Donovan Dennis.

The list of Cojanu's wins features no major scalps.

His most recent fight was a comfortable knockout win over China's Zhi Yu Wu last December.

That fight took place on the same day that 25-year-old Parker (22-0) claimed the vacant WBO belt, beating Mexican Andy Ruiz by majority decision in Auckland.