Larry Ellison, the largest outside financial backer of Musk's deal to take over the social media company, was subpoenaed as part of the lawsuit against Musk.
Ellison made a $1 billion contribution to Musk's bid.
Ellison was subpoenaed as part of the lawsuit over Musk backing out of his purchase of the company.
Ellison, a long-time Musk ally and a board member from this year to this year, pledged $1 billion to the CEO of the electric car company through his trust.
The trust's official was subpoenaed by the social network last week.
Forbes did not get a response from representatives for Ellison.
The company accepted Musk's proposal to take the company private. Musk filed paperwork July 8 to pull out of the deal over claims that the company did not give proper data about the number of accounts on the platform. A Delaware judge is being asked to force Musk to close the deal after he withdrew.
Ellison is the sixth wealthiest person in the world. Ellison has a 1.5% stake in the company. The largest fortune in the world is held by Musk.
The trial between Musk and the social networking site will last five days. The case promises a lot of drama, and Bill Savitt, the top lawyer in the case, called Musk a liar during a virtual hearing to set the trial date.
The company won a bid for a quick trial.
Larry Ellison was subpoenaed in the Musk buyout battle.
Larry Ellison gave $1 billion for Musk's takeover of the social networking site.