A spokeswoman at the National Hospital for Neurology and Neurosurgery in London, said the super-bantamweight was still in a "critical but stable" condition.
She said the 22-year-old boxer's condition had not improved during the day and he was still on a ventilator in intensive care.
Oliver, who was recently named Young Boxer of the Year, had a three-hour operation on Saturday to remove a blood clot after being knocked down in the 10th round as he defended his European title against the Ukrainian Sergei Devakov.
He was treated for 15 minutes in the ring before being stretchered away to Charing Cross Hospital, apparently unconscious. He was transferred to the neurological hospital for emergency treatment.
Doctors have said that if he survives he could be found to have suffered brain damage.
The seriousness of his condition has sparked renewed calls from the British Medical Association for boxing to be outlawed.
But Tony Banks, the Sports minister, yesterday rejected the demand as unrealistic. "Going for a ban is not the answer to this situation and it certainly isn't one that the Government is contemplating. But I do believe that there is a case to look at the way that boxing is organised."