If not = might or probable? (repost as I left out important information sorry)

"He is one of the best soccer players, if not the best." =

"He is one of the best soccer players, and probably the best."

or

"He is one of the best soccer players, and might be the best."

I think it definitely means

"He is one of the best soccer players, and might be the best." However, it could also mean:"He is one of the best soccer players, and probably the best." in some circumstances. Though, in the end, it means that you think there is a possibility that you are the best. It may also mean you think you are probably the best, but you may also think that there is a low chance you are the best. If anyoen can correct me, that would be great.