this happened to my Madden NFL 11 disc. Easiest thing to do is put it into a CD Sleeve instead of it's case. My Madden 11 still works to this day, and it has a 90 degree 1/2" crack on it. DONT mess with it, just leave it, and take good care of it from here on out and you should be fine.
If you have to put it in the case, press the tab down BEFORE you place the disc on it, instead of just mashing it into the case till you hear a 'click'. This will prevent damage to the disc, and only takes 1 extra second

. It's a nice habit to get into, for all your games sake.