Organisers of the Ready Steady Gallop community mass art event in Hamilton said that they were saddened to report that the sculpture at Chatelherault in Hamilton had been damaged.
The artwork is one of 25 created by local artists and decorated in a variety of styles which have been dotted around the area to form a trail, which has won the backing of the local community.
Police have launched an investigation into the incident.
Local Labour councillor Monica Lennon said: "Everyone is shocked and angered by what has happened. The police are following a positive line of enquiry and CCTV footage is helping with this.
"I know the community will get behind Ready Steady Gallop even more now so let's all pull together to make the project a big success for Hamilton."
Gareth Walker, manager of the community group Hamilton BID, said "We hope the people of Hamilton and visitors to the area enjoy viewing all of the other great pieces of art placed across the trail. Whilst disappointed by the weekend's vandalism, we don't want people to be disheartened, so are calling for the people of Scotland to get behind this project and ensure the remaining sculptures are seen by as many as possible prior to the auction in September."
Gerry Campbell, general manager of South Lanarkshire Council's leisure and culture department, added: "This horse had quickly become a very popular attraction at Chatelherault, especially among families taking their kids there to enjoy the facilities at the park.
"It's very sad that a few mindless individuals think it is OK to ruin the fun enjoyed by so many others. Hopefully the police investigation will be successful in tracking down the culprits.
"We will do what we can to support any effort to replace the horse."
The event is being held to raise money for the Kilbryde Hospice.