Kubrat Pulev says he will not step away from his shot at the world heavyweight belts and warned Anthony Joshua "you either fight or vacate the title".
The Bulgarian is mandatory challenger for Joshua's IBF title but their planned bout on 20 June was postponed.
It led to talk of Pulev being paid to step aside so Joshua could face Tyson Fury for all four heavyweight belts.
"I can't understand why we are still postponing instead of fixing a date and venue and getting to work?" said Pulev.
"Enough is enough. I can't wait to win this fight.
"I see how people are afraid of me and are trying to face someone else before me. That's not how a real world champion should act."
Pulev was due to face Briton Joshua in 2017 but withdrew because of injury and was also in mandatory position when Joshua lost to Andy Ruiz Jr in June 2019.
Joshua holds the IBF, WBA and WBO belts and has talked of his desire to face WBC champion Fury, who is due to face Deontay Wilder for a third time when boxing returns following its shutdown because of the coronavrius pandemic.
It would appear the two British heavyweights will need to wait and win their respective fights with neither Wilder nor Pulev appearing likely to accept 'step-aside' money.
"I did it once when I didn't have to do it for Joshua to have his second match against Ruiz Jr. Everything was against IBF's rules, but I compromised," said Pulev.
"A year has passed and they always have a reason to postpone, not to fight against me. There are two options. You either fight or vacate the title."
When and where a contest between Joshua and Pulev can take place is unknown because of the uncertainty caused by the coronavirus outbreak.
Pulev's manager has said venues - including a Roman amphitheatre in Croatia - were being discussed.
Pulev, one of Bulgaria's most popular sportsmen, suffered his only career defeat when he challenged for the IBF heavyweight title in 2014, losing to Wladimir Klitschko in Hamburg on a fifth-round knockout.
His record stands at 28 wins from 29 bouts, while Joshua has 23 wins from 24.