Doctors treating a boy with brain damage who is at the centre of a life-support treatment dispute think it is "very likely" he is "brain-stem dead", the High Court heard.
Archie Battersbee, 12, was found unconscious at his home in Southend, Essex, on 7 April.
Doctors at the Royal London Hospital in east London said his life-support treatment should end.
Archie's parents Hollie Dance and Paul Battersbee disagree.
A medical specialist told judge Mrs Justice Arbuthnot that tests showed no "discernible" brain activity and also raised a number of concerns from the team treating Archie.
The specialist, who cannot be named, said there was evidence of "significant areas of tissue necrosis".
"We believe that it is very likely that he is brain-stem dead," she said.
A spokeswoman for Archie's family told the court his family was praying for miracles.
Ella Carter told Mrs Justice Arbuthnot that relatives were aware he had suffered a "catastrophic" brain injury and a "natural" death would be easier to come to terms with.
The court previously heard that Archie suffered brain damage during an incident at home, which his mother believed may have been related to an online challenge.
Archie has not regained consciousness since.
Lawyers representing the Royal London Hospital's governing trust, Barts Health NHS Trust, have asked Mrs Justice Arbuthnot to decide what next step is in Archie's best interests.
Archie's family's legal team have argued that his heart was still beating and said there was an issue about whether "the correct procedure" had been followed.
On Monday, their lawyers also raised issues about whether the family's views had been taken into account.
A campaign organisation called the Christian Legal Centre was supporting Archie's family.
The final hearing for the case is being held in the Family Division of the High Court and is expected to end on Wednesday.