Brett and Naghmeh King’s lawyer revealed the “desperate” couple are considering “demands” against the hospital from which they took their five-year-old son last Thursday.
It came as the Deputy Prime Minister said he believes it is “not appropriate” to “throw the full force of the law” at the Kings, while it also emerged that one of Ashya’s brothers has seen him in hospital in Malaga.
The couple, who were arrested in Spain after Ashya was taken from hospital without doctors’ consent, have spent another night away from him.
A judge in Madrid has ruled that they must be held for up to 72 hours while the court considers whether to grant a British extradition request.
Juan Isidro Fernandez Diaz, the couple’s lawyer in Spain, said they are “so sad”, adding: “They are going to prepare legal demands against the hospital in Southampton. Legal action will be against the hospital.”
Mr Diaz told BBC’s Radio 5 Live that the couple “wanted the very best for their child”.
He said: “They never thought that they committed any crime in the UK.
“The child is in perfect conditions. All the doctors said (there was) no problem with the child to travel from England to Spain because the father knows (how) to give treatment to the child.
“We are saying the boy is not in danger. The big brother is with the boy and he is in perfect conditions.”
Mr Clegg’s intervention came amid growing calls for the couple’s release from detention, with an online petition attracting more than 80,000 signatures.
He told BBC Breakfast: “My heart goes out - and I’m sure every mum or dad will have the same response, which is, as far as I can make out, this is a family in a state of real anguish who have taken this exceptional step of moving their sick child to another country because they think that’s what is best for their child.
“We can debate whether it is or is not but that seems to be their motive and those are not motives I can argue with.
“That’s why I personally think that throwing the full force of the law at Mr and Mrs King, who appear to be doing what they believe to be best for their own family, I don’t think is an appropriate thing to do. But that, at the end of the day, is for the police and the CPS and others to decide.
“But that’s my personal view and I do hope, for that reason, it’ll be resolved.
“A little boy is on his own in a hospital, doesn’t speak Spanish, is cut off from his parents and his siblings and I would like to see him together with his family as soon as possible.”
He told Sky News “consular assistance” is being provided to the family
He added: “My understanding is that Ashya’s older brother did spend some considerable time yesterday afternoon and evening with him in hospital, and the Crown Prosecution Service have said they are looking at this case urgently from top to toe.
“I very much, as a person, an individual - I’m not making a political pronouncement here - I understand people’s widespread reaction, which is that you can debate whether that is the right treatment or not for this little boy, but for heaven’s sake keep this little boy and his parents and his family together.”
The boy is being treated in a hospital in Malaga and his grandmother and brother have criticised the way his parents are being treated.
The family took him from Southampton General Hospital last Thursday and travelled to France with him and his six siblings before heading to the Costa del Sol in southern Spain.
Mr King, 51, and his 45-year-old wife were arrested in Velez-Malaga on Saturday night.