Police were called at 8.23pm on Tuesday, 19 November to Fircroft Road in South West London.
A man was reported to have been approached by a group of men who threw a liquid at him before stealing his car and driving off.
Police attended with London Ambulance and London Fire Brigade also attended.
The victim, believed to be aged in his 20s, has been taken to hospital as a precaution. The substance was tested at the scene and was found to be water.
No arrests at this early stage.