Illness forced singer Madonna to delay the second date of her new Re-invention tour in Los Angeles by 24 hours.
Madonna kicked off her new world tour in Los Angeles on Monday
"Madonna has the stomach flu and was ordered by her doctor to rest this evening," a statement posted on her official website on Tuesday said.
The superstar kicked off the 50-date world tour in Los Angeles on Monday. The show will travel around the US, Canada and Europe.
Earlier this week the singer called off plans to play in Israel in September.
The brief message on her website said tickets for Tuesday's concert at the LA Forum would be honoured on Wednesday instead.
Promising the singer would be "back at 100%", the statement said "she can't wait to entertain her fans".
The singer will take a 100-strong entourage around the world
The third and final Los Angeles concert will be on Thursday, after which the tour will move on to Las Vegas and Anaheim, California.
Madonna defended her decision to cancel her proposed Israeli dates during an interview broadcast on Monday.
"If I had my way, I'd go - my manager wouldn't let me," she told US entertainment show Access Hollywood.
But the 45-year-old mother of two conceded "it's not a good idea to go there and do concerts", saying the shows had been scrapped because of the "attack on the leader of Hamas" in March.
BBC correspondent Peter Bowes called Madonna's first concert on Monday "a politically-charged and highly energetic show".
The concert featured graphic video images of US soldiers and injured children that were questioned by some members of the first-night audience.
More than 750,000 fans are expected to see the show as it makes its way across North America and Europe.
During the tour, Madonna will make a documentary chronicling the behind-the scenes action for a later cinema release.