Jackson announced his comeback shows in March this year.
Pop star Michael Jackson has delayed the opening four nights of his This Is It UK tour at London's O2 arena.
Concert promoters AEG Live said the delay was necessary because the singer needed more time for dress rehearsals.
The first show, on 8 July, has been pushed back by five nights. Three other July dates will not take place until March 2010.
Fans, who were told of the rescheduled dates in an e-mail, have reacted with a mixture of anger and support.
"What difference is a week going to make in the grand scheme of things?" wrote Pam A on a Michael Jackson messageboard.
"I had plane tickets booked from Canada," wrote a fan calling themselves janmic.
"I'm supposed to be returning home on July 9th. I am really not impressed."
The affected dates are as follows:
8 July - moved to 13 July, 2009
10 July - moved to 1 March, 2010
12 July - moved to 3 March, 2010
14 July - moved to 6 March, 2010
President of AEG Live, Randy Phillips, said the delay had been prompted by Jackson and his creative director, Kenny Ortega.
"Kenny and Michael are, at the same time, both creative pioneers and perfectionists," said Phillips in a statement.
"This show has grown in size and scope, thereby necessitating more lead time for manufacture of the set, programming the content for the massive video elements, and, most importantly, more time for full production and dress rehearsals.
"As much as we agonised over this change in the original schedule, we are sure the fans will understand when they experience the level of entertainment Michael Jackson intends to deliver."
Ortega, who worked on two of Jackson's previous tours and directed all three High School Musical films, apologised to fans.
"I know what the fans expect and myself and the team want to deliver a flawless production.
"We apologise to all disappointed Michael Jackson fans and remain extremely dedicated and focused on creating an exceptional live music experience."
Jackson's previous tours have featured magic, pyrotechnics and jetpacks
In an email to fans, Ticketmaster and AEG Live said: "We wanted to ensure that all of Michael's fans attending the concerts get the same quality in staging and level of entertainment."
"It is AEG Live's sincere hope that those lucky enough to have purchased tickets will have enough time to change their personal schedules and travel plans if they are coming from outside of London.
Full refunds are also being offered to those who cannot make the re-arranged concerts.
In March, tickets for Jackson's 50-date residency at the O2 completely sold out.
Hundreds of fans queued at the venue as tickets went on sale to the public and over a quarter of a million people queued online.
Around 750,000 fans have bought tickets to see the veteran pop star.