Jackson had asked to testify by a video link from the U.S. because of an unspecified illness. But his lawyer, Robert Englehart, informed the court Thursday that Jackson "has been cleared by his medical advisers to travel in two days' time."
The singer is scheduled to give evidence at the High Court on Monday.
Sheik Abdulla bin Hamad Al Khalifa, the second son of the king of Bahrain, says Jackson reneged on a contract for an album, a candid autobiography and a stage play after accepting millions in advances. Jackson claims the money was a gift.
Jackson, 50, and the Bahraini royal first made contact when the King of Pop was fending off accusations of child molestation in California and Al Khalifa offered to help him. Once Jackson was cleared of the charges in June 2005, Al Khalifa invited him to the small, oil-rich Gulf state to escape the media spotlight.
Al Khalifa, an amateur songwriter, says the pair even moved into the same palace to work on music together.
But Jackson dropped the project in 2006, leaving Bahrain and pulling out of the contract. Al Khalifa's lawyer says the sheik considered the move a betrayal.
The soft-spoken sheik took the witness stand Thursday, agreeing when Jackson's lawyer described him as a "devoted fan of Western pop music" and an extremely wealthy man.
"I would see myself as somebody who is very fortunate, yes," said Al Khalifa, 33.
He rejected Englehart's suggestion that Jackson was emotionally and financially fragile. Part of Jackson's defense is that the sheik took advantage of his vulnerability and lack of business acumen.
"Michael is an individual who is very switched-on," Al Khalifa said. "He is a fantastic intellectual."
"There's nothing unusual about him?" asked Englehart.
"No," Al Khalifa said.
The money at issue includes $1 million paid by Al Khalifa into the account of Jackson's personal assistant, Grace Rwaramba, who is due to give evidence later.
"You are an exceptionally generous person," Englehart told the sheik.
Al Khalifa replied "thank you," but denied the $1 million had been meant as a gift.
"To me it was never seen as a gift," Al Khalifa said. "Many a time he confirmed to me he would pay me back through our venture."
Al Khalifa says he gave Jackson millions of dollars in all to help shore up his finances and subsidize Jackson's lifestyle in the small Gulf state — including more than $300,000 for a "motivational guru."
Al Khalifa's lawyer, Bankim Thanki, said Al Khalifa considered the money an advance on the profits Jackson would reap from their pop music project.
Jackson's lawyers are arguing that the musician wasn't bound by the deal because the contract was signed on behalf of 2 Seas Records, a venture which never got off the ground.
The case is being tried in London by mutual agreement and is due to conclude early next month.