Last winter our breeder buck had a crack on the inside of his outer claw. I trimmed that side down shorter than the other side and in a week or two he was 100% better. Also had another that must have poked something on the inside of his knee and got an abscess. Had a buck fawn get an abscess above his hoof. Either way we had to knock them out to see what the problem was. If there is no obvious swelling and it just started I would maybe give it a handful of days and see if he gets better. He could have twisted it chasing or fighting. If he is not using it at all I would probably go ahead and knock him out.
we did not knock our buck with the cack in the toe down til mid/late Jan
He really took a hit on his score because he limped for about a month and a half but, he was all we had to breed with so we didn't want to knock him out til the does were bred