Assange, who has been living in asylum in the embassy for more than three years, has been suffering from a "deep pain" in his right shoulder since June. His doctor has advised he undergo an MRI scan.
Assange, who is Australian, took exile in the embassy to avoid extradition to Sweden, where he is wanted for questioning related to alleged sex crimes. He denies the allegations.
"The UK and Sweden are clearly violating international law," Assange's attorney, Carey Shenkman, told RT in a televised interview. "The UK is effectively brushing off its international obligations."
According to Shenkman, both the UK and Sweden are contravening legally binding accords, including the Covenant of Civil and Political Rights and the European Convention on Human Rights, both of which grant the right to medical treatment.
"What they are doing in reality is making Assange choose between his asylum and getting medical treatment. No person should ever have to make that choice," Shenkman added.
He also fears being extradited to the United States for WikiLeaks’ publication of thousands of classified documents.