Sounds suspiciously like the start of a Dupuytren's Contracture.
Think that's probably premature. His lump appeared after a long layoff following a sustained period of training. A priori it's much more likely to be a build-up of scar tissue than anything else.
The doctor who looked at it immediately said it was an irritation on the tendon sheath, which was close to the A1
There are two dots, because it does move depending on if I stretch out my hand, or if I am more claw like. There are no indentations or folds. I have had a mild case of dupuytrens in my right hand for quite a few years now, but it's located much further down in the palm of my hand. It flared up, and basically never got any worse, so I'm not worried about it these days.
good lick with this.