The rights group reported on Tuesday that Al-Singace was prevented from attending a previously scheduled doctor’s appointment.
Al-Singace, who is serving a life sentence for his role in Bahrain’s 2011 uprising, is disabled.
He suffers from a series of long-term health problems including disc problems in the lower back and neck, heart complications, nasal sinus inflammation and an enlarged prostate.
Throughout his time in detention, Al-Singace has been subjected to torture and various other forms of ill-treatment, leading to a further deterioration in his health.