What could be the cause of severe burning in the inner tissue of the ankle?

Tarsal tunnel. Sounds like a classic tarsal tunnel syndrome but there is usually a medical cause ie low thyroid, leg swelling, trauma, arthrisits etc.
Nerve or tendon. This could be nerve irritation on this area as burning pain is often from the nerve. But this may also be tendinitis or degeneration. A period of rest and good supportive well cushioned shoes is a good start but if pain persists or worsens, see your doc.
Nerve. This could be a neuropathy or issue with the nerves in your ankle. They could be impinged at the ankle, at the knee, or in the low back by a bulging disc. Or, if you have a condition like diabetes, it can cause this, but usually on both sides. Doct.
An entrapped nerve. There is a condition called tarsal tunnel syndrome. You may have this.