Mary J Blige and Chris Brown will not be performing
Plans for a Michael Jackson tribute concert in Vienna have been dealt a blow after previously announced stars say they will not be performing.
Representatives for Mary J Blige, Chris Brown and Natalie Cole said none of the three would be at the event on 26 September at Schoenbrunn castle.
However organisers have played down the lack of confirmed performers.
"The star is Michael Jackson - it's not about name dropping and who else will be there," producer Georg Kindel said.
Speaking at a press conference earlier this week, Jackson's brother Jermaine - who is also organising the tribute concert - told reporters that up to 25 performers had been lined up to sing.
But Karynne Tencer, a spokeswoman for Blige, said although the singer wanted to perform, "she had a previous commitment in Milan" at a Gucci fashion show.
Brown, who is on five years' probation for assaulting his former girlfriend, Rihanna, would need a judge's permission for any international travel, a Los Angeles court spokeswoman said. No motion to do so has yet been filed.
A spokeswoman for Cole said the 59-year-old could not be there because she will be attending an event in Tennessee for the Dalai Lama and can not make it to Vienna in time.
Maureen O'Connor said concert organisers had contacted Cole, "but she was never committed to do it".
It leaves only a few performers still confirmed to sing at the show, including Sister Sledge, Akon and German boy band US5.
A list of confirmed acts is due to be announced in Vienna next week, after Jermaine Jackson has personally confirmed who will attend.
"It seems that there is a lot of confusion regarding the confirmed talent for the tribute - we are rechecking and confirming each artist personally," Kindel said.
Jackson's mother, Katherine, pledged her support for the concert in a video message on the event's official website to quash rumours of a family feud over the event.
"I'm sure the show is going to be fantastic and I'm looking forward to seeing you there," she said.
Organisers said they were expecting 65,000 fans - who have paid up to 512 euro (£448) - to attend.
Jackson passed away in June after suffering a cardiac arrest.