What will happen if I machine wash a stuffed animal that says surface wash only?

My son's lovey toy (the one that he sleeps with, carries everywhere, pretty much never lets go of) says that it is surface wash only and specifically says not to submerge in water, but it's getting to the point where it just seems too gross and I have to do something besides wipe it down with a cloth. I would like to put it in the washing machine to get it really clean, but I don't want to ruin it since he's so attached to it. Any suggestions? Thanks!