The World Boxing Council (WBC) said that Lennox Lewis must face Mike Tyson before considering other opponents it was reported today.
Following Tyson's failure to secure a licence to fight in Nevada, Lewis said that he would not rule out fighting the official IBF challenger Chris Byrd on April 6th, the date originally scheduled for the Tyson-Lewis bout.
But WBC president Jose Sulaiman was quoted on the BBCwebsite, saying: "We just cannot allow this, because it would go against the WBC's board of governors.
"At our annual convention in 2000, we rated Mike Tyson the number one contender. It was a unanimous vote. During our annual convention of 2001 we ordered the mandatory defence," Sulaiman said.
Lewis, the IBF and WBC champion, said he hoped to reschedule the fight with "Iron Mike" for a later date, as Tyson is free to seek permission to fight in other states or countries beyond Nevada.
"We did not say that the fight should happen in any particular place, and when the promoters registered the fight with us, they never mentioned any city for the venue at all," Sulaiman said.
Possible locations raised for the $150 million fight - the richest in history - include Los Angeles, Manila and South Africa.
"This is the fight the world wants to see...if it is in April, May or June, the fight must be held. The people of the world want it," Sulaiman added.
In addition to Tyson's licensing difficulties and concerns over his mental health, rape allegations also hang over his head. Las Vegas police have confirmed that they have applied for a sexual assault prosecution to be brought against Tyson.