A spokesman for Mr Lee’s party said medical staff suspected injury to his jugular vein, which carries blood from the head to the heart. Mr Lee would have to undergo surgery as they were concerned about further bleeding, the spokesman, Kwon Chil-seung, said.

“After being transferred to Seoul National University Hospital, we plan to operate quickly. We strongly condemn the attack and consider it a clear act of democracy destruction,” he said.

Mr Lee, 59, currently holds a seat in Incheon in South Korea’s legislature. He is widely expected to run for a seat in the next general election, which will take place in April.

He narrowly lost the 2022 presidential elections – by a mere 0.73% difference in votes – to Mr Yoon, making it the closest presidential race in South Korean history. He is widely expected to stand in the next presidential elections in 2027.

Since losing the vote, he has been indicted on corruption and breach of trust charges, with prosecutors accusing him of allowing private developers to profit illegally from a property project while he was mayor of Seongnam, a city of 1 million people to the south of Seoul. Mr Lee has denied those charges, calling them politically motivated.