The 64-year-old was a guest at the opening of a new Beijing Easyhome store in the city of Zhongshan, Guangdong province, when an assailant rushed at him wielding a knife.
He arrived in Hong Kong late Saturday night and was admitted to Adventist Hospital.
Zhongshan police on Saturday evening identified the suspect as a 53-year-old local resident surnamed Chen, who they said had been diagnosed with schizophrenia. He was detained at the scene. A fruit knife was used in the attack, which left Yam with a 2cm-wide, 3cm-deep gash to his abdomen and an injured hand, the statement said.