Hi my dad has been having pain on the inside of his right foot right above the arch for sometime now what could be the cause of his pain? thank you

Tibial Tendinitis: The area you are describing is very possibly the posterior tibial tendon, the major arch supporting tendon in the foot and ankle. More than likely, he has a strain in the tendon, perhaps from wearing a pair of shoes lacking support or with excessive wear. He should avoid barefeet and flat shoes, and seek a consultation from a podiatrist for treatment which might include nsaids and orthotics.

Strain: He could be having pain at the navicular or the tendon do to strain on the arch of the foot.