It says coronavirus disruption casts “significant doubt” on its ability to continue as a going concern.
However, net losses widened as it ramped up spending on marketing, technology and staff.
The amount spent by Monzo customers also rose to £10.9 billion, up from £3.6 billion the previous year.
However, the business warned that it expects growth to slow in 2020.
“We’ve seen organic customer growth slow as word-of-mouth drops, and we’ll see reductions in revenues and higher credit losses,” co-founder Tom Blomfield writes in the report.