[Eliot Ness]

Like the others I would tend to leave it alone for now.  You'll have to pull the speaker board to see if it has just pulled away or is actually torn.  I suspect it is torn and for a good match you'll need to replace all of the cloth as already mentioned.

One thing I will suggest if you plan on keeping this set is to consider buying some grille cloth now while it is still available.  We had most of our supply dry up a year or two back when a manufacturer closed their doors, so while we currently have a supply I wouldn't take for granted that it will be around forever.