A soldier had a substance believed to be acid thrown in his face and was slashed with a knife during a robbery near his barracks.
Police found the unnamed victim, believed to be in his 30s, near Cavalry Barracks in Hounslow at 16:35 GMT on Tuesday.
The victim required hospital treatment but his wounds are not thought to be life-threatening.
No arrests have been made, police have said. Enquiries continue.
An Army spokesperson said: "We are aware of an incident that took place in Hounslow involving a serving soldier."