It happened after a fight broke out in Paddington in the early hours of Sunday.
The 19-year-old victim, named in reports as rapper Jelal Edmonds, and his mate had just left the club when they became involved in a row with two others, at the intersection of Oxford Street and South Dowling Street.
Police said a number of punches were allegedly thrown and the teenager was stabbed in the torso during the fracas before security officers intervened.
Panapa Iafeta, 20, who appeared with his friend on the singing show, told News Ltd the stabbing happened after a launch party for their new single.
‘He just sank down like he was in a slow motion movie,’ said Mr Iafeta. ‘Then he lay on his back. When I got to him his eyes just kind of closed.’
Mr Edmonds, who performs as Lazy J, was taken to St Vincent’s Hospital in a critical but stable condition.
Two men, aged 21 and 22, were arrested nearby before being charged with affray. They were granted conditional bail and will appear in Downing Centre Local Court on November 12.
Mr Iafeta and Mr Edmonds appeared on The X Factor in 2010. The release of their single has now been postponed, News Ltd reported.
From: Sky News Australia
Photo: beat100.com