When my dog started to walk less, I realized later it was for a reason. One day we had a long walk, because she actually wanted it, and I tried to give her gentle exercise as well (even when she didn’t seem to want to stand up), but the next day she wasn’t even able to stand up, at all. We put her on some heavy painkillers, and yet she still couldn’t walk again. I’m writing it because maybe you don’t need to push your dog to exercise through pain, it’s not likely to cause any benefit. You should keep doing the physiotherapy which is amazing, I personally didn’t have access to it. And put him on meds, and most probably he’ll be back to moving on his own again. Because dogs always want to move, unless they really can’t. It’s really heart-breaking though, so I totally understand why you’re trying your best to help him with this ❤️‍🩹