AEG Live has now made Friday's event free of charge.
A statement published on the festival's Web site this morning read: "Following Sir Elton Johns cancellation of all upcoming shows from his current European tour including his much anticipated show at Barclaycard presents British Summer Time, Hyde Park this coming Friday due to appendicitis, AEG Live and The Royal Parks confirm that the show will go on with the remaining stellar line-up for free and existing ticket holders will receive a full refund."
AEG Live said existing ticket holders for July 12 will automatically receive a full refund, with the full value of original ticket orders credited to the original payment method within seven working days.
James Russell, head of events and filming at The Royal Parks, said: "I know that many people were looking forward to seeing Elton John perform on the Great Oak Stage this Friday and we wish him well.
"We still have a fantastic line-up for Friday night and this gives us the opportunity to extend our free offering for this event - giving more fans the opportunity to see and experience everything Barclaycard presents British Summer Time Hyde Park has to offer."
Elvis Costello and Ray Davies have been named as the festival's headline acts for Friday, and AEG will be making more tickets available.
Tickets for the Rolling Stones performance on Saturday have sold out, however tickets for other days remain on sale, for acts such as Russell Kane, who performs tomorrow.
Fans who plan to attend Friday's concert are invited to print out free tickets at