Ouch, that's not good! There are a few things you can try, short of a full blown rotoscope application. I'd like to see a frame grab of this. If it is small enough, or in the correct place, SliceX from Coremelt has an object remover plugin that works really well.
Basically, you apply a shape, any shape, preset or freehand drawn, around the bad area. Then you use offset controls to move what actually covers that area. It works great in some cases, not so much in others. Here are where you can see samples of what it does.
Outside of that, you're going to need some serious rotoscoping work done. There is no magic "replace these pixels" button, unfortunately.