Madonna was forced to call off a concert in the US after falling ill with laryngitis.
The Girl Gone Wild singer - who is currently on her MDNA world tour - was due to take to the stage at the American Airlines Centre in Dallas, Texas on Saturday but had to pull out after becoming unwell.
A message on the star's website said she was suffering from "severe laryngitis".
It read: "Under doctor's orders, the Material Girl has been put on complete vocal rest for the next 36 hours. All tickets for the October 20th show to be refunded at the point of purchase. Tickets purchased online will be refunded directly."
It added that the Queen of Pop "regrets any inconvenience to her fans".
Madonna, 53, has been at the centre of several controversies since hitting the road. She came in for some flak after revealing her breast and showing off her bottom on stage earlier in the tour, and last week some fans in Colorado complained after the superstar used guns during a performance.
A gunman shot dead 12 people during a Batman screening at a cinema in the state in July.
Madonna started her show at the Pepsi Centre in Denver with a gun scene, which she has used in previous performances, and KUSA-TV said it received several calls from concert-goers saying they were offended.
In a statement before beginning the tour, Madonna said she does not condone the use of guns. She said she is using the guns as symbols of intolerance and "the pain I have felt from having my heart broken".