A US judge will decide whether R&B singer Chris Brown can perform at the Michael Jackson tribute gig in Vienna later this month, it has emerged. Jermaine Jackson announced that Brown was part of the concert's line-up on Wednesday, but now there is doubt over whether he will be allowed to attend. Brown, 20, was sentenced to community service after he admitted to assaulting his ex-girlfriend, Rihanna, last month. There are concerns his legal commitments might clash with the gig. "Chris Brown is working out some situations but he definitely expressed to us that he wants to be here," Jackson said at a press conference in London. "It's just up to what he's going through with his court case right now - but he's definitely going to work that out and be here." Jackson said that, despite the negativity publicity surrounding Brown's court case, he was happy for the singer to take part. "People make mistakes and he's a wonderful performer and during these times people need support and that's really important," he said. Georg Kindel, who is co-producing the show with Jackson, said it was thought that a judge would decide whether Brown could leave the US. During the August court case, Brown was ordered to stay at least 100 yards away from Rihanna for the next five years. The judge said violation of the terms would be taken "very, very seriously". Mary J Blige, Sister Sledge and Natalie Cole will definitely perform at the concert, which has been put together in honour of Michael Jackson, who died in June, aged 50. No other acts have been added to the bill so far, although Jackson said he was confident that Stevie Wonder would agree to sing. He also hinted that the Jackson family may reunite on stage at the concert. Organisers said they were expecting 65,000 fans to attend. Tickets went on sale last month for the event, which takes place on 26 September. Credit: BBC