Oleksandr Usyk has requested an extension on negotiations to fight Joseph Parker due to injury, promoter Frank Warren has told Sky Sports.
Usyk was recently ordered by the WBO to defend his belt against mandatory challenger Parker after defeating Daniel Dubois to become undisputed heavyweight champion of the world.
Alternatively, Parker could face the winner of Moses Itauma against Dillian Whyte should Usyk vacate the WBO title.
"He (Usyk) put a letter in yesterday stating that he's asked him for an extension period, because he's injured, before being ordered to do anything," Warren told Sky Sports News.
"Whatever happens the fact of life is Joseph Parker will either fight as champion if Usyk vacates or he will fight Usyk for the title.
"If Moses or Dillian win, they're in the No 1 spot and if the fight with Usyk and Parker doesn't happen then Joe (Parker) will have to fight the official number one contender."
Usyk became a three-time undisputed champion, twice at heavyweight and once at cruiserweight, in July when he knocked out Dubois to add the Brit's IBF belt to his collection.
He had stated prior to the contest that he believed he had two more fights left in his, so far perfect, professional career, with a prospective bout against Parker seemingly representing the second.
Usyk was, however, also linked to a potential trilogy fight against Tyson Fury in 2026 after the Gypsy King underlined his wish to seek revenge following back-to-back losses to the Ukrainian.
"His camp have written asking for a period of time before he has to defend the title," Warren continued.
"We'll see what happens and the WBO will put a statement out on this today or tomorrow, I've been informally told what the position is. The most important thing is to focus on Saturday, it's a very important fight."
Parker was denied a shot at the IBF title earlier this year when Dubois withdrew from his scheduled title defence due to illness during fight week.
The New Zealander subsequently knocked out last-minute replacement Martin Bakole to keep his world title hopes alive.
On Saturday the attention turns to another aspiring world champion when the highly-rated Itauma encounters the experience of Whyte, who is looked to derail his younger opponent's development while also setting up another big night of his own in the latter years of his career.
