As its the two smaller finger on your hand it sounds like it is related to your Ulnar nerve.
It may not be Diabetes at all as you play tennis so much the chances are it is that which
is the cause. The nerve runs through your shoulder and is most exposed as it passes
through you elbow, it doesn't take a lot to compress it and get similar symptoms.
It's still worth getting it checked out with the doctor I did when I experienced it. For me it turned
out I had lost sufficient weight that I was managing to bundle up into a smaller ball (thats relative)
whilst asleep and in turn compress the nerve. So now on the odd occasion I wake with numb fingers
I no longer panic and just stretch