One of the ringleaders of the Hatton Garden jewellery raid is in intensive care after falling ill in custody.
Brian Reader is being treated for "a number of issues" at the Queen Elizabeth Hospital in south-east London, according to his solicitor Hesham Puri.
Mr Puri said it was "unlikely" his client would be able to attend the sentencing hearing, listed for next month, for his role in the £14 million raid.
It is understood Reader, 76, had a number of outstanding health issues when he pleaded guilty to conspiracy to commit burglary last September.
Reader - involved in the £26 million gold bullion Brink's-Mat robbery three decades earlier - was convicted for his part in the "sophisticated" and meticulously planned break-in at Hatton Garden Safety Deposit Ltd in central London over the Easter weekend last year, believed to be the biggest burglary in British history.
Dubbed "the guv'nor", he was convicted alongside John "Kenny" Collins, Daniel Jones and Terry Perkins, who all pleaded guilty to conspiracy to commit burglary.
Carl Wood and William Lincoln were convicted of conspiracy to commit burglary and conspiracy to conceal, convert or transfer criminal property.
Hugh Doyle was found guilty of concealing, converting or transferring criminal property.
Another thief, known only as "Basil", let his co-conspirators into the building by opening the fire escape from inside. He has not been identified.
The gang stashed the jewellery, gold and cash behind skirting boards at various houses and Jones even buried several bags of jewellery with urns of ashes under memorial stones at a cemetery.
Reader has been held in custody at Belmarsh prison in south-east London since his conviction.
He is listed to be sentenced with his six accomplices at Woolwich Crown Court on March 7.
A Prison Service spokesperson said: "An HMP Belmarsh prisoner was taken to hospital on 24 February. He remains there in order to receive treatment for an ongoing medical condition.
"Appropriate security measures are in place."
A hospital spokesman said he was unable to comment due to patient confidentiality.