It is possible that your husband has a cartilage/meniscus problem in his knee, related to his previous footballing days. Arthroscopy would help to diagnose this and very often one can definitively deal with the problem as well. However, a clinical examination is very necessary, to consider the various possibilities. For this, you could either consult a rheumatologist (that is, a physician specialising in the management of joint problems) or an orthopaedic surgeon.