The mastermind behind the Hatton Garden jewellery raid may only have months to live, a court heard.
Brian Reader, 77, suffered a stroke while being held at Belmarsh Prison.
He and six others were due to be sentenced in a three-day hearing, starting on Monday, over the £14m Hatton Garden safety deposit box heist.
His barrister James Scobie said Reader, who pleaded guilty to conspiracy to commit burglary, was too ill to appear via video link from the London prison.
The hearing started without Reader.
Mr Scobie said: "He [Reader] had what turned out to be a second fall in Belmarsh prison, which resulted in him being left for two days without proper care and then ultimately ending up in a critical care unit at Woolwich hospital, having had a stroke."
The pensioner may not "have many more months to live," the lawyer added, asking for his sentence, due to be handed down at Woolwich Crown Court, to be adjourned.
Judge Christopher Kinch said Reader did not need to be in court for the sentencing hearing and that he would revisit the matter on Wednesday when more information on the prisoner's condition should be available.
The court heard Reader has a history of prostate cancer, was treated for septicaemia and has a growth on his face which is potentially cancerous.
Mr Scobie also told the court Reader's recovery was not aided by the nine armed officers who guarded him in hospital.
The lawyer also said he was concerned Belmarsh Prison was not capable of adequately caring for his client, who has reduced vision in his right eye and problems hearing.
He said: "He [Reader] is a double Category A prisoner, which we view with nothing other than scorn given his age and other factors."
A report from a doctor indicated one of the reasons Reader had a stroke was because the secure unit he was in did not have "sufficient capacity" to look after his health concerns, said Mr Scobie.
Opening the sentencing, prosecutor Philip Evans said the "group of thieves" brought with them a "great deal of experience in planning and executing sophisticated and serious acquisitive crime".
Mr Evans asked the judge to reconsider the sentence for count one in the trial, conspiracy to burgle.
The maximum sentence for burgling a non-dwelling property is imprisonment for 10 years, he said, which should be reconsidered as the plot was "of the utmost sophistication, that was many years in the planning".
He added: "It was designed to achieve the maximum possible return for the minimum possible risk, and, the prosecution submit, plainly fits within the broad range of the worst type of this offence which comes before the court, particularly bearing in mind the low maximum sentence."
He said it would be "contrary to the interests of justice" to follow the relevant guidelines and urged the judge to take the 10 year sentence as a "starting point".
Ringleaders John "Kenny" Collins, 75, Daniel Jones, 61 and Terry Perkins, 67 pleaded guilty to the offence last September.
Carl Wood, 59, of Elderbeck Close, Hertfordshire, and William Lincoln, 60, of Winkley Street, Bethnal Green, were convicted of conspiracy to commit burglary and conspiracy to conceal, convert or transfer criminal property after a trial at Woolwich Crown Court.
Plumber Hugh Doyle, 49, of Riverside Gardens, in Enfield, was found guilty of concealing, converting or transferring criminal property between 1 January and 19 May last year.