Deputy spokesman for Thailand's main opposition Democrat Party was viciously assaulted in front of his home in Bangkok and in critical condition in hospital, Bangkok Post online reported on Tuesday.

Police said the attack on Ramet Ratanachaweng occurred in Bang Na district on late Monday night.

When investigators arrived at the apartment complex they discovered a pool of blood next to a car. The victim, later identified as Ramet, had already been taken to a nearby hospital.

Ramet sustained a deep wound to the head when he was hit with a hard object. He was still under intensive care on Tuesday.

Tankhun Jittitsara, spokesman for the Democrat leader, told reporters that Ramet was attacked by two men who arrived on a motorcycle.

According to the medical team, Ramet suffered a skull fracture and severe concussion. Doctors would have to determine if there was any internal bleeding and he would remain on a ventilator.

As a legal adviser to the major opposition party, Ramet is involved in many cases.

Investigators suspect the attack was carried out by people who stand to lose in one of the legal disputes, but have not ruled out personal grudges.