The symptoms as mentioned in your post can be attributed to musculo-skeletal injury.
X ray of knee joint will be helpful in clinching the diagnosis.
Symptomatic relief can be obtained by heat therapy
, application of analgesic
& muscle relaxant
gel, intake of analgesics like Diclofenac
(to be taken after food) + Pantoprazole
(to be taken 30 minutes before meals).
Supplements of Calcium & Vitamin D can be included in his diet which will help in strengthening of bones.
If symptoms still persist, it will be better to consult an Orthopedician for proper clinical examination.
Till then, maintain adequate hydration & nutrition status, take proper rest and avoid stress.
Wishing a Good Health.