Barton was due to go on trial at Manchester Minshull Crown Court over the incident, but changed his plea shortly before the scheduled start.
The 25-year-old admitted one charge of assault occasioning actual bodily harm to Dabo when they were playing colleagues at City.
Barton - whose victim Dabo was in court to hear him plead guilty - will be sentenced on Tuesday morning.
Since bursting on to the football scene in April 2003, Barton has been making headlines both on and off the pitch.
But he always escaped the courts and prison - until this year.
It is the third time Barton has been in court in 2008, but his bad behaviour stretches back more than four years.