Madonna Struggled with Fever For a Month Before Serious Bacterial Infection

Madonna battled a low-grade fever for a month before her body could no longer take it, collapsing and needing serious medical care ... TMZ has learned.

Sources familiar with the situation tell TMZ, Madonna mostly ignored her symptoms and never got checked out by a doctor because she was laser focused on rehearsing for her upcoming tour ... working her butt off to get ready to perform.

Our sources confirm the Page Six report Madonna collapsed before she was rushed to the hospital Saturday, where she ended up spending days in the intensive care unit. We're told her doctors believe the unreported fever was a sign of the infection, which worsened because it was left untreated.

While our sources say Madonna is doing better and is expected to recover from the non-life-threatening illness ... there's still concern for the "Vogue" singer.

We're told Madonna's doctors, and those around her, are worried she's going to go against doctor's orders and push to start her world tour ASAP ... even though she's going to be required to rest up and recover for a while.

Our sources feel Madonna is going to want to get back to work too soon and go on tour, which could cause more health issues. We've confirmed Madonna is back home after being released from the hospital ... she was discharged Wednesday night and is recovering at her New York City residence.

Madonna's longtime talent manager Guy Oseary says her health is improving, but we're told the infection is more serious than is being let on and it got worse because of her nonstop work schedule.