South Korean opposition leader Lee Jae-myung was stabbed in the neck on Tuesday while speaking to reporters in the South Korean port city of Busan, Yonhap News Agency reported.
The Yonhap Agency published a photo showing the politician lying on the ground with a handkerchief covering his wound
Mr Lee was still conscious when he was taken to hospital. According to the same source, the attacker was arrested on site.
Democratic Party leader Mr Lee lost to conservative Yoon Suk Yeol in South Korea's 2022 presidential election.
Mr. Lee, a former worker and governor of Gyeonggi Province, the country's most populous province that surrounds Seoul, had proposed novel measures including a universal minimum income and free school uniforms.
But his candidacy for president was marred by a series of scandals.
Mr Lee had been criticized in particular over a real estate transaction that was considered dubious. There were also rumors that he had ties to the mafia and his wife was accused of illegally using public funds.
In September 2023, Mr. Lee escaped arrest after a court rejected a prosecutor's request to remand him pending trial on various corruption charges.
He is suspected of corruption in connection with a company that allegedly illegally transferred $8 million to North Korea.
Mr. Lee is also accused of losing 20 billion won ($15 million) to a company in the city of Seongnam (northwest), where he was mayor.