The star gave fans in Lisbon just 45 minutes' notice that her show on Sunday night was being called off.
"We regret to inform you that Madonna is unable to perform this evening," an email informed ticketholders at 19:45. She had been due on stage at 20:30.
"Sorry I had to cancel tonight," the star wrote on Instagram, "but I must listen to my body and rest!"
It is the eighth time Madonna has had to cancel a show on her current world tour, which sees her playing smaller, intimate theatre venues.