The band are due to play Radio 1's Big Weekend in Swindon
Singer Tulisa Contostavlos, from pop band N-Dubz, is being tested for swine flu after falling ill on board a flight to Greece, her manager has confirmed.
The 20-year-old from north London was taken to hospital in Athens.
Miss Contostavlos has undergone tests to determine if she has the virus, which has now been confirmed in 15 cases in the UK.
The band's manager Jonathan Shalit has told the Press Association her band mates are "all very worried about her".
He added that he had "no idea how she got ill" but "the nature of being a singer is that you meet and shake hands with a huge amount of people".
The three-piece, which includes Miss Contostavlos's 21-year old cousin Dino 'Dappy' Contostavlos and their childhood friend Richard Rawson, 22, have enjoyed huge success this year.
They currently occupy the top spot in the singles chart, featuring on Tinchy Stryder's hit, Number 1.
The band are also due to play Radio 1's Big Weekend in Swindon next weekend but the appearance could be in jeopardy if tests prove positive.