Call the Vet IMMEDIATELY!!
For future reference, if it is a hoof problem the best way to tell what and which hoof, is to WALK the horse on rough gravel, and the horse will accentuate the lameness. The horse will "pull" the head up to help move the hurting hoof.
If it is a muscle injury the horse will favor one side over another, JUST LIKE WE DO.
If the horse will not walk on anything by the front tip of the hoof, it's probably an absess, usually caused by dirty/wet conditions. This is totally unnecessary if the stall hasn't been cleaned. =/ That's usually 3 or more days of NO stripping out manure and urine and making the horse stand in it.
My boy, Buster Brown (24/7 turnout, 4 acres), pulled up lame on the right front last week. It's been SO MUDDY, that I suspect he was running and slipped. Almost all better, now.
Thanks everyone for the help...great thoughts. He is a very kind horse. From the comments I believe it has something to do with his leg and not his feet. I have already called a vet and will hopefully get him in good enough shape for my kids to ride....thanks!