The 23-year-old American said she would be in the August edition.
The 23-year-old noted other athletes who have appeared in the magazine, including Olympic swimmer Amanda Beard and former volleyball player Gabrielle Reese.
"I'll be the first tennis player ever. That's kind of cool," Harkleroad said.
"There's a few reasons why I did it, but I can't really go into it right now," she added. "But like I said, I really didn't think it was that big of a deal. I'm proud of my body. I stay in shape and try to stay fit."
Williams, an eight-time Grand Slam champion, said she respected Harkleroad's decision to pose for the men's magazine, but ruled out her own pictorial.
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