Yanaran Johnson, 21, of Leichhardt, faced Parramatta Bail Court charged with three counts of aggravated sexual assault of the 50-year-old woman at her home in western Sydney in the early hours of Friday.

A police fact sheet tendered to the court said Mr Johnson was staying at the house overnight after visiting the woman's full-time carer.

The fact sheet tendered to the court said Mr Johnson entered the woman's room just after midnight on Friday and stood over her with an erect penis.

He asked her to perform fellatio, which she refused to do.

Police allege Mr Johnson then forced his penis into the woman's mouth, then she bit it.

The fact sheet said Mr Johnson then threatened the woman with a large butcher's knife, which he held to her throat then allegedly anally and vaginally raped her.

At 5am the carer was woken by the woman having a seizure in her room, and noticed bruising on her face and called an ambulance.

The victim, who police said had physical disabilities which caused problems with her mobility, was treated for numerous injuries at Liverpool Hospital.

Mr Johnson was denied bail to appear at Liverpool Local Court on May 28.