Police believe the two men are known to each other and ruled out antisemitism as a motive for the attack.
A statement from the Metropolitan Police said officers had responded to reports of a dispute at the synagogue in Golders Green Road, and found a man suffering from the effects of being sprayed with what was believed to be CS gas.
Police said the man was taken to hospital but that his condition was not life-threatening and his injuries not life-changing.
The Community Security Trust confirmed that, following discussions with police, the incident was “not a matter of wider concern”.
A spokesman for the local branch of the Shomrim neighbourhood security group said that, following the incident, the shul, commonly known as “Reb Chuna’s”, was immediately evacuated by volunteers from Shomrim and the Hatzola ambulance service.
