The courtroom clash between two Las Vegas personalities - casino mogul Steve Wynn and " Girls Gone Wild" founder Joe Francis - is finally moving forward but without a star witness.

Music legend Quincy Jones was excused from testifying on medical grounds in the pair's slander trial expected to get underway next week, the New York Daily News reports.

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In a written order, Los Angeles Superior Court Judge Joanne O'Donnell granted Jones' request "in light of the declarations of Mr. Jones and his physician," according to the paper.

Jones, 79, had been dragged into the bitter, more than three-year court feud between the two by Francis, who calls Jones one of his best friends and claims that he showed him an email from Wynn in which the mogul threatened to murder Francis over a gambling debt.

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In the alleged email from Wynn, the mogul allegedly plotted to have Francis, 39, killed by bashing him "in the back of the head with a shovel" and then digging him a sandy grave away from the Las Vegas Strip, according to court documents filed in Los Angeles Superior Court in 2010.

Wynn, 70, who owns the hotel where Prince Harry recently partied in Vegas, denies that such an email exists and included Jones, a 27-time Grammy Award winner, on his witness list.

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Legal experts say that without Jones, Wynn's defense is weak.

"Jones is the key to this case," legal analyst Larry Walters told ABC News. "Without Jones there is no death threat because there is no email that has been produced."

The court battle between the two moguls began in 2009 when Francis, who has a reported $150 million fortune and has faced charges of tax evasion, child abuse and prostitution in the past, refused to pay a $2 million debt owed to one of Wynn's casinos.

After Francis publicly accused Wynn of deceptive practices at his casinos, Wynn sued him for defamation. In February a Nevada judge ruled in favor of Wynn and ordered Francis to pay $7.5 million.

Wynn's camp argues that Francis' latest allegations against Wynn of threatening murder amount to slander because of their impact on his reputation.

"Joe Francis says he saw emails that don't exist," Wynn's attorney said in a statement to ABC News. "Everything is a lie."

Francis had no comment on the case when contacted by ABC News.