The goose probably has some type of arthritic condition if it has sustained an injury to the foot/leg from years ago. As long as the goose can enter and exit the water, fly, feed, bathe and rest, he/she should be fine.

Although the arthritis is painful, many waterfowl have it from sustaining injuries earlier in their lives as well as from old age as in humans and other animals.

Additionally, even though it may be painful, if the goose has been around for 3 years, then it must be doing okay. If an animal/bird has an injury/painful condition, illness, etc., other members of the flock/herd may shun the bird/animal, but also it can be that the goose itself has chosen to stay away from any possible fights or encounters that it cannot defend or escape. Now that it is mating/nesting season, hormone levels are high and fights could result. The goose may be waiting for things to settle and then will look for its own mate/area of the habitat later during the mating/nesting season. The Regal Swan