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."


