looks like a little mat burn to me. put an antibiotic on it every day and tape it up if your going to train. No biggie, I have had mat burn that has lasted quite awhile also. Either that or its Leprosy and if thats the case then you will get to hang out at your own island!
Are you new to grappling or returning after a long break?
It looks like a simple mat burn and the skin does toughen up a good deal with time. Until then, enjoy having your socks get stuck in that shit. Tape it up (perhaps with a bit of plastic over the wound itself) when you're on the mat until it heals.