"He got my finger pretty good," the mayor said.
Bloomberg was wearing gloves at the time so the damage wasn't very severe. He covered the cut with a napkin until a doctor could take a look at it, the New York Daily News reported.
The attack occurred when Bloomberg tried to pick up the groundhog after failing to lure it out of its wooden home with a corn cob at the Staten Island Zoo.
Mayoral spokesman Stu Loeser told WPIX-TV there was no concern about rabies because Chuck was raised in captivity and has been isolated from other animals.
Bloomberg appeared to be taking a light-hearted view of the incident, joking later that it was a case of "a terrorist rodent who could very well have been trained by al-Qaida in Afghanistan."
For the record, Staten Island Chuck -- just like Pennsylvania's Punxsutawney Phil -- saw his shadow. So, in accordance with Groundhog Day lore, winter will last another six weeks. But Chuck had better be spot-on with his forecast, or else, the mayor intimated.
"If Chuck embarrasses us, this is going to be a very long winter for the Staten Island Zoo," he said.