Could be a picture of my thumb
I have the same exact issue. In fact, that could be a picture of my own thumb. Polysporen works to help it heal. If you're like me, you can't just stop playing to let it heal because I play in 3 different leagues and have to play. Mine has to heal while i play so I use the white athletic tape like the trainers for my high school football team used to tape up ankles. I tear it into strips about ½ inch wide and about 8" long, and wrap it around the callus when I have to play. If you've ever seen Nadal's left hand you'll see most of his fingers and thumb are usually taped when he plays too. The athletic tape stays in place pretty well even when you are sweating.
If you know anyone who sells Melaluca products, there's a hand lotion called Renew that's helpful in preventing the callus from cracking. Mine only cracks now when I forget to use this cream.