I am thinking that might be a manufacturing stain - if it does not smell and it has been dry - I would use it.
If it is washable, I would soak it for a couple of hours with a dab of mild detergent, spin, rinse, and dry gently.
My machine will let me do that - don't know if yours will.
If the stain is still there, and it would not show, I would use it.