Italian premier Silvio Berlusconi is in pain, having trouble eating and remains in hospital following an attack by a mentally ill man that broke his nose and two teeth, doctors said.
Doctors said they had ordered Mr Berlusconi, 73, to cancel or reduce public appearances for two weeks, meaning he will not attend the climate talks in Copenhagen.
They had previously said he would be released from hospital on Wednesday, but it is now expected to be Thursday afternoon.
Mr Berlusconi's personal doctor said he was not worried that the prime minister's overall health was in danger from injuries he suffered when a souvenir metal statuette of Milan's cathedral was hurled into his face at close range at a rally in the city.
Police tightened security around Mr Berlusconi.
The prime minister is fending off a sex scandal and legal troubles and he has decried what he calls a "climate of hatred" against him.
The Press Association has contributed to the report.