My crab might be sick or wounded

[wodesorel]

Personally, I think it would stress the crab more to separate it. Whatever he has isn't contagious, it's a side effect of the physical injury on his claw. Moving him someplace smaller is going to be hard to maintain since it's hard to know when he'll need to molt again. He'll need access to both types of water deep enough to submerge, and room to move around, just like any other hermit. If the other crabs in the tank are leaving him alone, he really is fine where he is.

[Clypeatus]

What I did to my PP when she molted in my 20 gallon tank is to put glass from extra picture stands to prevent other crabs from getting her. You can also get a 10 gallon aquarium at Walmart for approximately $13.00. You can also use a plastic bin with a lid. It is not best to use a wood enclosure because wood will rot due to the high humidity.

Hope that helps.