LOS ANGELES—Insurance underwriters considered the late pop music icon Michael Jackson “fragile” and a difficult risk, which likely influenced the availability of coverage for a sold-out 50-concert stand in London, several entertainment insurance observers said.

“It was well-known that he was quite fragile,” said David Foreman, group director of underwriting at Ark Syndicate Management Ltd. in London. “It would be very difficult for him (or the producers of his concerts) to buy insurance. We all know how fragile, physically and otherwise, he was.”

Ark did not provide limits for Mr. Jackson's planned shows, which were set to begin July 13 at the O2 Arena in London. But Mr. Foreman participated in providing coverage for a past Michael Jackson show and was among thousands of people holding tickets for the shows. Before joining Ark, Mr. Foreman was chief underwriting officer of Wellington Underwriting.

London-based Robertson Taylor Insurance Brokers Ltd. placed contingency insurance for some of the London concerts for Los Angeles-based AEG Live, an entertainment conglomerate and producer of the planned shows, sources said.

Robertson Taylor, which specializes in placing coverage for music and entertainment risks, is a unit of Oxygen Holdings P.L.C. A spokeswoman for Oxygen declined comment.

Some contingency coverage for the tour was written by Lloyd's of London syndicates, several London sources said.

The losses to the contingency market—which includes event cancellation coverage—are likely to be limited, though, because underwriters declined to cover the entire tour, sources said. Instead they provided coverage for a limited number of Mr. Jackson's initial performances.

“We can confirm that some insurance for Michael Jackson's concert has been placed in the Lloyd's market, but any losses are not likely to be significant,” a Lloyd's spokesman said.

Talbot Holdings Ltd., which manages Lloyd's syndicate 1183, confirmed in a statement that it underwrote some of the Michael Jackson contingency coverage but said its maximum exposure net of reinsurance was less than $3 million. Talbot is a unit of Validus Holdings Ltd.

Reports indicated AEG would self-insure the shows if it could not obtain insurance.

Mr. Jackson died suddenly last week in Los Angeles, where he reportedly was rehearsing for the London shows. The 50-year-old reportedly suffered cardiac arrest. The Los Angeles coroner's office conducted an autopsy Friday and ordered tests, including toxicology, that a spokesman said would take four to six weeks to complete.

The singer, known as the King of Pop, produced a string of hits starting in the early 1970s and his 1983 album “Thriller” remains the highest-selling record of all time.

Concert producers, ticket distributors and merchandise vendors typically buy insurance to protect against losses that result when a show fails to go on, either because of problems with a performer or the venue.

But underwriters typically require proof of insurability through a medical examination before providing the size of limits that would have been sought by producers of Mr. Jackson's tour, said Brian Kingman, managing director in Los Angeles for Gallagher Entertainment, a unit of brokerage Arthur J. Gallagher & Co.

The outcome of such an exam would shape policy terms and conditions such as potential coverage exclusions that would determine any payout, Mr. Kingman said.

AEG said that Mr. Jackson successfully underwent such a medical examination, and friends reportedly said he recently appeared in good physical condition.

Underwriters also are concerned about longer tour schedules because the likelihood of problems mounts over time, especially for large and complex productions, said Mary Craig Calkins, a partner specializing in entertainment industry and insurance recovery at Howrey L.L.P. in Los Angeles.