Shivu Munishetti slashed his private parts and hand with a blade, officials at Hindalga jail where he and the other death row convict Jadeswamy Rangashettti are lodged, said.
Shivu was being treated at the jail and might be shifted to district hospital, the officials said.
Jail officials had said earlier that they had made all arrangements to hang both of them most likely on August 22 after President Pranab Mukherjee rejected their mercy petitions on August 13.
In a letter purportedly written by Shivu, he claimed that he came from a respectable family and was innocent.
He was falsely implicated in the case and wanted justice, Shivu said in a letter to the media released by one of his relatives.
Shivu and Jadeswamy were sentenced to death in 2005 for raping and murdering an 18-year-old girl at Bhadranhalli of Chamarajnagar district.
Their conviction by the District and Sessions court was upheld by the High Court and Supreme Court.After the apex court confirmed the death sentence in 2007, both had sought Presidential mercy.
Thirty-six persons are awaiting gallows in the jail, including five associates of sandalwood smuggler Veerappan, who had struck terror in the forests bordering Karnataka and Tamil Nadu before he was shot dead in a joint operation by the two states.
