The rapper, who used to date his bandmate Tulisa Contostavlos, is said to have been unable to pay his tax bills.
Newspaper The Sun claims to have seen official documents, which show that 26-year-old Fazer - real name Richard Rawson - was declared bankrupt on 4 December.
Fazer rose to fame alongside Tulisa and her cousin Dappy - Costadinos Contostavlos - in 2008 following the release of their debut album Uncle B.
During their career, N-Dubz won four Mobo Awards and an O2 Silver Clef Award. They also received a Brit Awards nomination.
The band released their greatest hits album in 2011, however they have not worked together since.
In February, Dappy avoided a jail sentence following a brawl at a petrol station.
Meanwhile, it was announced last week that Tulisa is to be charged with a drug offence following an alleged incident in the summer.
Her rep has indicated that she will plead not guilty to the charge.