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Serena Williams headed to Hyde Lounge in Hollywood with pal Brittny Gastineau on Monday night ... and looked like she needed to "hyde" her head!

Williams kept her head down, which showed off her bald spot on top. We love you, Serena, but that needs to get taken care of!

Other than the hair affair, the tennis star looked sexy in a see-through top and leather jacket.

This isn't the first time we've seen celebs out with embarrassing (or should we say emHAIRassing?) bald spots! See who else is a member of The Bald And Not-So-Beautiful club after the jump!