The hole is “not especially large, but it is noticeable”, and for the time being it has been covered with sellotape while it awaits a more technical repair, the Milan edition of Corriere della Sera reported.
The painting is a large oil canvas from the 18th century by an unknown artist. It depicts Capellino Isimbardi, an ancestor of the family who used to own the building in which it is on display, and which is now the seat of Milan's council. Its value is estimated at several thousand euros.
Councillor Roberto Cassago, 71, is the man responsible for the damage, which he caused by opening a bottle a little too vigorously during the gallery's Christmas celebrations.
An announcement from the council on Wednesday explained that Cassago “caused the damage involuntarily, and has taken the responsibility of paying for the artwork's restoration.”
They said that the painting had only suffered “minor damage; a rip of a few centimetres", which has been secured in anticipation of a complete restoration.
“The authorities took action in the days immediately after the event to begin all the necessary measures for the restoration of the painting, which should soon be returned to the town citizens,” the council said.