Britney Spears has been forced to cancel two Las Vegas shows this weekend while she recovers from an on-stage slip up.

The Womanizer singer tumbled on Wednesday night when her ankle gave way during a particularly energetic performance of her hit (You Drive Me) Crazy.

She had reassured fans that she was OK, but now her Friday and Saturday performances have had to be rescheduled following doctors’ orders to rest up.

Britney currently has a residency at Planet Hollywood on the Las Vegas strip, where she performs her Piece Of Me shows.

Earlier in the week, she had tweeted to let concerned fans know that she was fine after falling over.

In happier news for Britney, the artwork for her collaboration with Iggy Azalea has been released.

The pair have teamed up for Pretty Girls, with a music video based on the Eighties cult classic film Earth Girls Are Easy, and the track’s cartoon cover shows Britney riding a space rocket through the galaxy while Iggy’s animation poses in silver body paint.