Medial knee pain after a fall could be a medial collateral ligament (MCL) sprain/tear, especially if the knee was forced inward. Other possibilities include a medial meniscus injury, bone bruise, or less commonly a fracture.

It cannot be diagnosed reliably without an examination. Seek urgent assessment today if there is:

Until assessed: rest from impact activity, ice 15-20 minutes at a time, compression if comfortable, elevate, and use a support/crutches if walking hurts. Avoid twisting or forcing the knee straight.

Because this started after a fall last week and persists, arrange an in-person clinician or orthopedic assessment. An X-ray may be needed to exclude fracture; MRI is sometimes used later if a ligament or meniscus injury is suspected. Textbook sources list MCL rupture among key causes of medial knee injury after trauma, and radiographs are the first study when significant trauma or fracture is suspected (Bailey and Love's Short Practice of Surgery, p. 256-260; ACR knee-trauma guidance).

Pain only on bending the knee, with mild pain and no major swelling or inability to walk, is more consistent with a minor soft-tissue strain/bruise. On the medial side, this could involve a mild MCL strain or irritation of the medial meniscus. The medial meniscus moves and bears more load when the knee flexes, so it can hurt with deeper bending after a twist or fall. Miller's Review of Orthopaedics, p. 9298-9316

For the next 5-7 days:

Get examined if it is not clearly improving within 1-2 weeks, or sooner if swelling develops, the knee locks/catches, gives way, pain becomes sharp, or full bending/straightening becomes difficult. Do not self-test the knee by forcing it sideways.