Why Johnny Depp wasn't called to testify by Amber Heard's team

Johnny Depp was expected to return to the witness stand on Monday as his defamation trial against Amber Heard enters the sixth week. At the last minute, Yahoo Entertainment confirmed the actor would not be called by the Aquaman star's legal team.

"Calling Depp back to the stand would be as relevant to us as a bicycle to a fish," a source close to Heard tells Yahoo. "Everything Depp has testified up to this point has been irrelevant to the heart of this case, and there's no reason to believe it would be any different now."

There have been plenty of strange moments during the trial and Monday was no exception. The actress's team called Dr. David Spiegel as an expert witness, and during cross-examination, he was very combative with Depp's attorney, Wayne Dennison. One moment even caused the Pirates of the Caribbean star to laugh and put his head in his hand in disbelief.

Spiegel and Dennison were sparring over whether Depp used an earpiece on set. The psychologist testified that the actor's use of the device could be a sign of cognitive decline from heavy drug and alcohol use over the years.

"If I was giving a lecture and I was fed my lines, I would think there's a cognitive deficit," Spiegel said.

Spiegel went on to say he doesn't believe "actors are routinely given their entire script through earpieces, I find that hard to believe." When pressed if he has any evidence Depp was fed his lines through an earpiece, the psychologist said "that's what I read in the court review." (Earlier during the trial, Depp's friend and longtime sound technician, Keenan Wyatt, testified the actor used an earpiece "all the time" — to listen to music or get fed a line after rewriting his dialogue.)

"Do you know whether Marlon Brando ever used an earpiece?" Dennison asked.

"Isn't he dead?" Spiegel replied.

Depp, who's been eating gummy bears and drawing doodles throughout most of the trial, put his head in his hand.

"So the answer is no, he does not use one now," the witness quipped.

"I used the past tense, sir," Dennison said.

"Oh, I'm sorry," Spiegel replied. "Again, I will concede to you I know nothing about acting. I will concede to you 100%. If that is the standard... I am wrong."

Spiegel was asked about calling Depp an "idiot" in his deposition.

"[Depp] was coming in from Europe for a deposition, video deposition that he gave, and he took an overnight the night before and what I think I said was... if you're going to do a major thing for a trial that you're involved with I would think you would be an idiot to come in the night before. So I didn't call Mr. Depp an idiot. I certainly called that planning idiot. I didn't call him an idiot," Spiegel said.

"I don't know Mr. Depp's IQ, I don't know his auditory functioning. So, therefore, if I said it — it was an idiot in planning which is what I meant to come across as," he added.

Spiegel testified he found Depp to display narcissistic personality traits. However, the psychiatrist never evaluated Depp and publicly commenting on the actor's mental state could be a violation of the American Psychiatric Association's (APA) ethics rules. That brought another tense exchange with Depp's lawyer.

"We might as well get rid of all the expert witnesses we've had throughout all of time for court proceedings because what you're saying, that unless a court orders it, and that's what you just said, or APA said, then, therefore, expert witness could not do an evaluation based on the observation of the medical records," Spiegel fired back.

Spiegel said he is not offering an "armchair diagnosis" of Depp.

"I have reviewed a lot of professionals, a lot of professionals and the evaluations and their treatment course, video depositions, picture deposition, court filings, emails. I've reviewed a whole lot of things that describe Mr. Depp and his behavior," he added.

Celebrity lawyer Chris Melcher, partner at Walzer Melcher, believes Spiegel's testimony was an "ethical violation."

"Dr. Spiegel's testimony started fine, discussing how drug and alcohol abuse can have an impact on personality, memory and impulse control. He should have stopped there, allowing the jury to potentially draw a conclusion that Johnny Depp's history of substance abuse contributed to the conflict between the couple," he explains. "But Dr. Spiegel went further, attributing psychological traits to Johnny like narcissism and saying Johnny was at risk of committing intimate partner abuse."

Prior to trial, the judge denied Heard's request for Depp to be psychiatrically evaluated.

"Spiegel reviewed records and somehow made conclusions about Johnny's personality. This was an ethical violation," Melcher says, citing APA rules. He explains it "was essential to conduct an evaluation before opining about Depp."

Melcher believes the jury may disregard the testimony "because of the damage done during cross."

Although Depp didn't take the stand on Monday, he will return to the witness box. Yahoo has learned he will be called as a rebuttal witness by his legal team, likely on Wednesday.

MORE: Amber Heard cross-examined about writing Johnny Depp "love notes" after alleged rape