If you are talking about a link where someone has posted negative about your brand or service (Negative Branding/Reverse Branding), then link is not at all negative and Google will give it a good weightage as it is considered as a customer review and if someone is writing negative then here is something serious. This is what Google thinks. But manytimes Google's Software review it carefully and decide what to do with it automatically.
Here you can use ORM to correct it. This will save the value of your brand. But a very few experts know how to do it effectively.