The pop singer Rihanna will not perform at a concert in Dubai scheduled for May 28, the same date that a court hearing is scheduled in Los Angeles for her companion, Chris Brown, The Associated Press reported. Yassin Matbouly, the managing director of an entertainment agency in the United Arab Emirates, said that he had been told by Rihanna’s management that “it was inappropriate timing for her to have a public concert” on that date, according to The A.P. In April, Mr. Brown pleaded not guilty to felony charges that he threatened and assaulted Rihanna during an argument in February. On Monday night, Rihanna made a public appearance at the Metropolitan Museum of Art’s Costume Institute Gala in New York. Mr. Matbouly said he would try to reschedule the concert.