Sorry to hear about Remi's leg! Is it a back leg or front? (I may have missed that if you mentioned it.) Have you checked his paws/pads/nails? It could be something as minor as a crack in a pad or a hangnail!
Oliver went through something similar with symptoms that would go away and come back, limping after running, etc. He began with a luxating patella which eventually led to a torn ACL. (Now, I'm NOT saying that is what Remi has!) Typically, with the torn ACL, a vet can feel through the knee (without X-rays) to determine if it's a tear. Oliver had TTA surgery for his tear in May 2012 and while it wasn't the easiest to go through recovery, it was needed and we made it through just fine. If for some reason it is a tear, I have a whole thread on here documenting Oliver's TTA surgery and his entire recovery. Feel free to hit me up if you need to but I am sending POSITIVE vibes that Remi will be just fine and it will be something minor. HUGS!!!!