Doctors have ordered Christina Aguilera to cancel her world tour after falling ill during a concert in Australia. The Fighter star, who is rumoured to be pregnant with husband Jordan Bratman's baby, suffered breathing difficulties at a gig in Melbourne on Friday (27Jul07) as part of her Back To Basics tour. Aguilera was forced to shorten her 70-minute set at the gig, dropping three songs from her set list, and was advised to cancel the two remaining dates in the city. Her second concert at Melbourne's Rod Laver Arena, scheduled for Saturday (28Jul07), was postponed until Sunday (29Jul07) - but the singer was deemed unfit to perform after medical examinations on Sunday morning diagnosed a viral upper respiratory tract infection with a high fever and abnormal coughing. A statement from the star reads, "I want to personally apologise to all of my fans for having to cancel my last two shows here in Melbourne. "Unfortunately, I have fallen ill with a bad flu virus. This is one of the best cities in the world to perform in and I am truly disappointed that I won't be able to share my show with you all. Thank you for all of the continued love and support, and I hope to perform for you all again next time."