Spears has apparently aggravated an old dance injury

Spears, 22, was treated after a scan showed floating cartilage in her knee, Jive Records said in a statement.

The knee "gave out" as she performed choreography scenes for her single Outrageous in New York on Wednesday.

Spears - due to begin a US tour on 22 June - was forced to cancel two shows in March because of a knee injury.

The injury occurred shortly after Spears had completed a scene with rap star Snoop Dogg at a Manhattan subway.

'Dance injury'

"She obviously took a wrong step and blew out her knee," a Jive spokeswoman said. "It was an old dance injury."

There was no immediate comment on the outcome of the surgery.

Spears' tour begins later this month in Hartford, Connecticut. Her latest album In the Zone was released in November.

The singer is also set to give her first concerts in China, which have been approved by the country's culture ministers on condition that she does not reveal "too much" skin on stage.

Five concerts in Shanghai and Beijing will take place later this year as part of her world tour.