Ganglion cyst: This is a common, benign lump that can occur on the foot, often associated with repetitive trauma or stress, such as that from playing soccer. The lack of pain, redness, itchiness, or discharge also supports this diagnosis, as ganglion cysts are typically asymptomatic aside from their presence.

Bursitis: Given the patient's active participation in soccer, bursitis (inflammation of a bursa, which cushions joints and reduces friction) is a plausible diagnosis. However, the absence of pain and redness makes it less likely than a ganglion cyst.
Lipoma: A benign tumor composed of fat tissue, lipomas can occur almost anywhere on the body, including the foot. They are usually painless and could fit the patient's symptoms.
Callus or corn: Repeated friction or pressure from soccer activities could lead to the formation of a callus or corn, which might be perceived as a lump. However, these are typically associated with some discomfort or pain, especially if they become thickened.

Soft tissue sarcoma: Although rare, sarcomas can present as painless lumps. It's crucial to consider this diagnosis to ensure timely treatment if present, despite its low likelihood.
Infectious or parasitic lesions: Certain infections (e.g., mycetoma) or parasitic infestations can cause lumps on the foot. The absence of symptoms like redness, itchiness, or discharge does not entirely rule out these possibilities, especially in individuals exposed to risky environments.
Foreign body reaction: If the patient has stepped on something that penetrated the skin and was not entirely removed, a foreign body reaction could occur, leading to a lump. This would be more likely if there was a history of such an incident.

Glomus tumor: A rare, benign tumor of the glomus body, usually presenting under the nail but can occur elsewhere on the foot. It's known for causing significant pain, which doesn't fit this patient's symptoms well.
Neurofibroma: Part of neurofibromatosis type 1 (NF1), these benign nerve sheath tumors can occur anywhere, including the foot. They are generally painless but are associated with other systemic findings.
Kaposi's sarcoma: A type of cancer that can cause lesions on the feet, especially in immunocompromised patients. The presentation is usually more complex than a single, painless lump.