Police investigate western Sydney assault

A western Sydney man has been found on his bathroom floor with significant facial injuries just one hour after he left a social gathering.

Police say the 30-year-old spent time with two women and another man at an Oatlands house on Saturday before he left about 10pm to return home.

When one of the women followed him to the house an hour later, she found him injured in the bathroom and he was taken to hospital.

Police believe the man was assaulted and have set up a crime scene at the home.