Donald Tsang Yam-kuen arrived at the Museum of History to open an exhibition.
A member of the radical League of Social Democrats rushed at him and apparently hit his chest.
Protesters also threw cooked rice at Tsang, as a symbol of the plight of the poor, but missed him.
After a medical check-up, Tsang said: "A protester ran at me and hit my chest. When I went for dinner I still felt a little bit of pain, so my wife asked me to have a medical check."
He said such violence was unacceptable in Hong Kong, where civilised behaviour and the rule of law were fundamental values.
A doctor at the Queen Mary Hospital said Tsang would feel the pain for a few days.
Tsang went to church and work as usual yesterday.
Lawmaker "Long Hair" Leung Kwok-hung said he did not see any physical contact between Tsang and protesters and that the league would meet the press to explain what happened.
The alleged attacker, Steve Wong Chun-kit, 25, was arrested and released on bail.
Legislator Regina Ip Lau Suk-yee, of the New People's Party, said she did not think the protesters had hit Tsang deliberately but they should behave more rationally.
Our readers' comments:
Lee Yuk-yu, 18, TWGHs Mrs Wu York Yu Memorial College
Hong Kong people always think they are more civilized than mainlanders. But the attack shows we are barbaric. It is shameful.
People are free to express their political views. They can write to government departments or newspapers. They can even protest or shout their opinions, but they should never attack anyone. If we are to solve our problems and maintain our image we must express our ideas in a legal and decent way.
Louise Pau, 17, Diocesan Girls' School
I couldn't say I was shocked by the attack on our chief executive. Lawmakers encourage violence. For instance, Leung Kwok-hung, known as Long Hair, is notorious for his unruly behaviour in meetings. I hope that in the future, political party members and protesters practise constraint and show more respect to government officials.
Charmaine Mirandilla, 18, recent graduate from YMCA of HK Christian College
Public dissatisfaction with the government is growing and Donald Tsang is at the forefront of it all. He has failed to defend the Hong Kong people's rights with regards to democracy. He is a puppet of Beijing.
The government is sitting on billions of dollars but Tsang has failed to redistribute even a small portion of this wealth to the people in order to alleviate their financial hardships. It is no wonder that Tsang has been attacked. I'm surprised it didn't come sooner!
Janet Tam, 16, St. Rose of lima's college
In my opinion, Tsang's attack is somehow exaggerating. Because his injuries was not so serious. This also shows that the security guard of the Chief Executive needs to improve inorder to protect him more comprehensively.
Arjun Sivakumar, 14, South Island School
In democratic set up public opnion on issues are bound to have mixed responses. It is basic human right to express our feeling and Hong kong has upheld itself as an autonomous region by allowing its public to vent their feelings in open forums vociferously. However it is the method of expressing your feelings that varies.
The current attack on our Chief executive Donald Tsang is a reaction to the recent budget proposals. While I can accept the feelings of the public in venting their displeasure, it is not a democratic practice to go on a physical aggresion. This is definitely not an acceptable way of expressing our feelings and is totally undemocratic to be condemned in all forms.
At the same time, it would have been a magnanimous act of genrousity and understanding, had the Chief Executive taken the issue in the right sprit and pardoned the protester. This would have shown the soft side of the governance while being empathitic to the people cause.