Pastor Yang Hua, the leader of Living Stone Church, is said to be "on the verge of paralysis" after medical staff at the detention centre where he is being held denied a request for injections to treat an infection.
Instead, the medical staff only provided Yang with painkillers.
After his lawyer visited the pastor on 20 and 24 March, Yang was transferred to a military hospital.
Staff at the hospital recommended his condition be treated with penicillin but it does not appear that Yang has been provided with the medication. Doctors warn that without treatment, Yang's legs may need to be amputated.
Yang's lawyers have written to Guiyang authorities asking for a review of the case and requesting that he is transferred to a fully functioning hospital.
His wife has not been granted permission to view his medical records.
Advocacy group Christian Solidarity Worldwide have condemned the treatment of Yang and his family.
CSW's Chief Executive Mervyn Thomas said: "The consistent denial of medical care to Pastor Yang Hua of Living Stone Church is inhumane and inconsistent with international standards on the rights of detainees.
"Pastor Yang has repeatedly requested medical treatment, and his lawyers believe his situation to be critical.
"We call on the Chinese government to release Yang Hua, to allow him immediate access to adequate medical care, and to investigate allegations of torture and ill-treatment in detention.
"We further call on the Chinese authorities to cease all harassment and restrictions on other church members, and to uphold the right to freedom of religion or belief for all."
Yang has been detained since December 2015 and was handed a prison sentence of two and a half years for "divulging state secrets" by a court in January.
Yang had attempted to stop police from removing a hard drive from the church after authorities raided his house church.
At the trial in January, Yang's lawyers claimed that the pastor had been tortured in prison by the government appointed prosecution.