Meralgia Paresthetica: This condition is characterized by numbness, tingling, and burning pain in the outer part of the thigh, but it can sometimes present with pain in the inner thigh due to the involvement of the lateral femoral cutaneous nerve. However, given the specificity of the question towards inner thigh pain, a more common cause such as Adductor Strain or Groin Strain might be considered the single most likely diagnosis, as these are common injuries in athletes and individuals who engage in physical activities that involve running, kicking, or quick changes of direction.

Adductor Strain: A common injury in athletes, especially those involved in sports that require quick changes of direction, kicking, or sprinting. The adductor muscles are located in the inner thigh, and strain or pull in these muscles can cause significant pain.
Groin Strain: Similar to adductor strain, a groin strain involves the muscles of the inner thigh and can cause pain in this area.
Osteitis Pubis: An inflammatory condition affecting the pubic bone and the surrounding muscles, which can cause pain in the inner thigh.
Stress Fracture: Stress fractures in the femur or pubic bone can cause pain in the inner thigh, especially with weight-bearing activities.

Aortic Aneurysm: Although less common, a ruptured abdominal aortic aneurysm can cause severe pain that may radiate to the inner thighs. This is a medical emergency.
Herniated Disk: A herniated disk in the lower spine can cause radiating pain down into the thighs, including the inner aspect, due to nerve compression.
Ovarian Cysts or Torsion (in females): Ovarian cysts or torsion can cause severe pelvic pain that may radiate to the inner thighs.
Testicular Torsion (in males): This is a medical emergency that can cause severe pain in the groin area, which may radiate to the inner thigh.

Neurogenic Tumors: Rare tumors that arise from the nerves, such as neurofibromas or schwannomas, can cause pain and other neurological symptoms in the affected area.
Inflammatory Arthropathies: Conditions like rheumatoid arthritis or psoriatic arthritis can cause pain and inflammation in various parts of the body, including the inner thighs, though this would typically be part of a more systemic presentation.
Chronic Exertional Compartment Syndrome: This condition involves increased pressure within the muscle compartments, leading to pain and swelling, typically after exercise. It's less common in the thigh but can occur.