Have you tried to potty train him. My girl used to do the same during the first week or two after I brought her home.
Have a look at this video for litter training. Does he sleep in this burrow where you found the pee spot?
Also, have you provided the little one with a sand bath? If so, check if it contains lumps of sand at the bottom. If it does, the odds are he is already using the sand bath as his toilet. If not, and he still pees in the burrow, place the sand bath in a corner nearest to the burrow and transfer the soiled substrate onto the litter tray as explained in the video. He'll pick the cue quickly.