The 18-year-old, who is the cousin of former club captain Steven Gerrard, had been the subject of interest from Serie A side Fiorentina recently but Liverpool want to keep the youngster.
Duncan's representative, Saif Rubie, says Duncan is being kept at the club against his will.
The Reds described Rubie's comments as "unfounded allegations".
In a lengthy statement released on social media, Rubie said: "This is not really dignified behaviour from a club with the rich history of Liverpool and one [at which] one of their greatest-ever players, Steven Gerrard, happens to be Bobby's cousin.
"It's a sad state of affairs that a club such as Liverpool can be allowed to get away with mentally bullying and destroying the life of a young man such as Bobby."
Enjoy you Scouse pricks!!