'The X Factor's Louisa Johnson's chances of winning the show have been dealt a blow after she was struck down by a "nasty" virus.

Louisa Johnson

Louisa Johnson

The 17-year-old star - who is clear favourite to win the competition - has been kept in isolation as a result of the bug, which also affected co-host Olly Murs, and is struggling to speak let alone sing.

A show source said: "Louisa is putting on a brave face but she can hardly speak. We're worried she could be too ill to continue next week. We couldn't give her a free pass to the final, there would be

uproar."

'The X Factor' bosses have urged contestants to stay in separate rooms in the house and have issued hand sanitiser to wannabes in the hope the virus will not spread further.

Olly has reported flu-like symptoms after being hit by a similar bug.

The source added to The Sun newspaper: "If any of the other contestants come down with the same thing we will really struggle. Olly is also sick and struggling. The bugs going round at the moment are really nasty."

Louisa confirmed on Saturday night's show that she was "not very well" and complained of a sore throat after performing her two songs - renditions of Justin Bieber's 'Love Yourself' and Labrinth's 'Jealous'.

She said after the programme: "I don't know how I got through the show, it was pure adrenaline. My throat is so sore. I can't speak or sing."

Despite concerns, Louisa remains odds-on favourite with all bookmakers to clinch this year's 'X Factor' crown in next month's final.