Following a "serious" bacterial infection that sent her to the hospital for several days, Madonna spent time in intensive care.
The illness has forced the legendary singer, 64, to postpone her tour.
She was reportedly found unresponsive on Saturday and rushed to the ICU where she was intubated.
Guy O'Seary, her talent manager, said in a statement: "On Saturday June 24, Madonna developed a serious bacterial infection which lead to a several day stay in the ICU.
"Her health is improving, however she is still under medical care. A full recovery is expected.
"At this time we will need to pause all commitments, which includes the tour. We will share more details with you soon as we have them, including a new start date for the tour and for rescheduled shows."
Her Celebration tour was scheduled to launch in July, with the first stop being Vancouver, followed by four shows in London in October and two in December.
The 84-date tour was planned to mark the 40th anniversary of the release of her debut album.
The last time Madonna performed at London's O2 Arena was in 2015, as part of her Rebel Heart tour.
Due to hip and knee injuries, the singer has previously been forced to postpone tour dates.
Announcing her Celebration tour, Madonna said: "I am excited to explore as many songs as possible in hopes to give my fans the show they have been waiting for".
After finishing her Sticky & Sweet tour in 2009, she was previously given a Guinness World Record for the highest-grossing musical tour by a female artist.