That this patch is infected. It sounds like it might be a fungus.
With all the steam, sweating at the gym etc, it is a possibility.

Covering over an infected patch with an occlusive ointment may make it
worse. Also staph is often on the skin, and can complicate things.

I'd do an antibiotic ointment like Neosporin first for a few days. If it does
not clear up, I'd add an antifungal like clotrimazole cream or Lamisil and see
what happens. Once cleared up/healed then any barrier ointment may work.
I prefer A and D ointment for this. But Aquaphor is good too.