Rajesh Talwar, father of murdered teen Aarushi, was admitted in the intensive care unit (ICU) of Apollo Hospital with multiple injuries on Tuesday after a grievous attack on him with a cleaver outside a Ghaziabad court.
His lawyer said the dentist may be unable to work again as his hands were slashed badly.
Talwar suffered a serious head injury with a major blood vessel being snapped.
His hands were also slashed as he covered his face to stave off repeated attacks by Utsav Sharma, the same man who assaulted tainted Haryana police chief S P S Rathore last year.
"Dr Rajesh Talwar has been admitted with injuries at multiple sites. He is being clinically evaluated and treated by a multi-disciplinary team of doctors in the Intensive Care Unit (ICU)," said a statement issued by the Indraprastha Apollo Hospital in the evening.
Talwar's lawyer Rebecca John earlier said he was undergoing surgery at the Apollo Hospital for his head injury.
The injuries on his hands would require extensive reconstruction surgery, she said.
"Dr Talwar was hit at least thrice by Sharma who accosted him suddenly," said an eyewitness.
The attack took place as Talwar was walking out of court after filing a protest petition against the CBI's closure report on the case.
Talwar could be seen holding his head in pain as blood flowed out.
The place was milling with hundreds of people, including television cameras, when the attack took place.
The court has adjourned the hearing to Feb 8. It has also ordered in camera proceedings of the case.
Aarushi, 14, was found murdered under mysterious circumstances in her parents' Jalvayu Vihar apartment in Noida, May 16, 2008.
Their domestic help Hemraj was initially suspected for the killing, but his body was found on the flat's terrace a day later.
Talwar was arrested soon after the murders but let off when investigators could not find evidence to nail him.