It could well be nothing & great you've got the vet. I would keep an eye on him & not let it continue for too long. Of course, some horses naturally lie down more than others, but they don't tend to all that much unless there's a problem. Does he still need to be locked up? Was he used to being locked up before the injury?
Did his feed change due to it? Are you just feeding him all those treats to try to get the medicine into him, or does he always get them? It's especially if he gets a high sugar diet &/or he's getting bute & antibiotics that he's become laminitic, so wants to keep off his feet. He could also be sore on the 'good' foot from compensating.
The vet should be the one that could give you an estimate on recovery time, as not only is he a vet, but he's attended the wound & we don't have a clue how serious or superficial it may be.