The British-Australian performer dedicated a composition at a 2024 MSO performance to journalists killed in Gaza, saying they had been deliberately targeted by Israel, and the orchestra responded by cancelling his next concert.
The pianist is suing the orchestra for unfair dismissal in the Federal Court.
Former managing director Sophie Galaise was accused of lying when she told the organisation's board that Gillham had withdrawn from the upcoming concert, knowing it had actually been cancelled.
"Like any human you use words, and for me this was probably interchangeable," she said, under cross-examination by Gillham's barrister Sheryn Omeri KC.
"I understand the difference, but this is what I wrote."
Dr Galaise was sacked a fortnight after the concert and had also been a respondent in the Federal Court case, but her dispute with Gillham settled in March 2025, while her separate Fair Work claim against the MSO has also been resolved.
When asked if she was concerned that Gillham's onstage comments were critical of Israel, Dr Galaise responded she was worried they had been made without the MSO's prior knowledge.
"This was not approved, it was a highly sensitive political message ... it would have some impact on our organisation," she said.
Gillham's lawyers outlined that among the MSO's various donors are the Gandel Foundation and Besen Family Foundation, both of which fund philanthropic work in Australia and Israel.
Immediately following a leadership meeting responding to the growing crisis caused by Gillham's concert, Dr Galaise was scheduled to discuss an upcoming MSO tour of Europe, funded by a portion of a $600,000 donation by the Gandel Foundation.
Dr Galaise was unsure, when questioned, whether she had told the meeting that taking a pro-Palestine stance would put the MSO's future funding at risk.
The MSO had spent months consulting stakeholders before it adopted a neutral position on the Gaza conflict, the court heard.
Under cross-examination, Dr Galaise disagreed that an internal briefing statement on the conflict was not objective and took a pro-Israel stance, because it failed to assign responsibility for Palestinian suffering.
Dr Galaise also disagreed she was determined to do what Jewish concertgoers and donors wanted, and that nothing would have made her rethink the decision to cancel Gillham's next concert.
"I was particularly concerned about maintaining a balanced position of neutrality," she said.
She also questioned the accuracy of meeting minutes read to the court, which noted that two MSO board members, including current chair Edgar Myer, had expressed interest in the orchestra adopting a pro-Israel stance.
The hearing also canvassed various classical composers including Chopin, Rossini, Schubert and Bach, with Gillham's barrister noting each of them composed music of a political nature.
Dr Galaise said she did not have any opinions about other composers using their music to express their political beliefs.
The hearing continues on Monday.
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