if you can get it out try and catch it but its probably too late, it wil just get mashed up in the cogs as its only plastic, you might want to do a gear oil change in a month or so and lots of bits will come out, you may have trouble selcting one of the gears at some point, i found that if this happened i set off in another gear i.e. second and then it dislodged it, dont try to hard to ram it into gear, don't worry though it shouldnt do any harm
