We have never given a swan an aspirin. Our vets prescribe Medicam so you will need to have a vet exam the cygnet. He may have sprained the leg, but if it is permanent, it is going to be extremely difficult for it to survive without being able to enter and exit the pond. The cygnet will need to be contained in an extremely sheltered habitat, usually a pen protected from predators and in a habitat with a zero entrance water feature to help it get in and out of the water. We are going to ask the webmaster of this site to contact you directly and provide you with a number of a swan breeder in Texas who might be able to help you. The Regal Swan