Ivan - is it just the lacquer that's scratched or does it go all the way through INTO the oak?
If it's just the lac that's damaged, and it's a small area, I'd be tempted to do a local repair to the scratch as a first attempt. Small artist brush, jar of lac/varnish, and try painting-in to build-up the layers. Care & a steady hand needed. If you get away with this method you're going to save yourself the task of following WYL's very good advice.
It is possible to 'raise the grain' of scratches/gouges in timber by the gental application of water or other liquid (small artist brush); this has the effect of swelling the wood thus 'filling' the scratch. Your problem is that if you wet oak it'll often dis-colour, this would pose a problem if your oak is very light in colour. With a rustic oak any slight discolouration might be acceptable.
At the end of the day you have to remember that it's a floor, it's going to get marked, scratched and scuffed - all of which, in my opinion, adds the attraction and character of wooden floors (just wait till the dog and the kids have used it for a while).