Where do you live. If in the plains then heat could be one reason why he is not that active. How old is he. If you live in the hills it can be a leech mark after falling off. The problem with TM is that they can bear a lot of pain and one really does not know what the problem or if he is in pain for quite some time. Monsoons invite a lot of skin problems. I have not seen the wond so cannot comment, but show it to a vet. You can also clean it with Betadine liquid and then apply some dusting powder for the wound to try up.
But if he is eating properly then it should be ok and if he is not limping. As for the exercise, do you make him run or does he do it yourself, plus what is the area he lives in farm house, tied or open etc.
I have had a lot of TMs in the past and they again are great dogs but can be stubborn and have a mind of themselves at times and have a tendancy to roam every once in a while so be careful.