Attorneys for Redstone's former girlfriend, Manuela Herzer, had issued a subpoena in New York to demand that Dauman make himself available for a Jan. 26 deposition in the contentious court case.
But Herzer's side suffered a legal setback late Tuesday.
New York state Supreme Court Justice Kathryn Freed ruled that Herzer and her legal team first "must show cause" as to why Dauman's testimony is necessary. Otherwise, the judge could quash the subpoena and issue a protective order shielding Dauman.
Freed set a hearing for March 15.
The date is important because Herzer's legal team had wanted to take Dauman's deposition before a Feb. 8 court hearing in Los Angeles.
That is when Redstone's lawyers with the Loeb & Loeb firm intend to argue that Herzer's petition should be dismissed.
Now it appears that Herzer's attorneys -- led by Pierce O'Donnell of the firm Greenberg Glusker in Century City -- will have to make their case without the benefit of a Dauman deposition.
Herzer's team still will be able to question the personal physician of Redstone, 92, and another doctor who examined him. Redstone is the executive chairman of Viacom and CBS Corp.
Herzer has asked a Los Angeles County judge to rule that Redstone is mentally incompetent.
She is challenging an Oct. 16 move by Redstone to remove her as agent in charge of the mogul's advance healthcare directive should he become unable to make decisions for himself.
That same day, Redstone appointed Dauman, his friend and business associate for nearly 30 years, as his healthcare proxy.
"We are confident that we will eventually get Philippe Dauman's sworn testimony," O'Donnell said in a statement. "It is just a matter of time."