NEW YORK: Serena Williams is the top tennis player in the world and an emerging fashion designer. But she still needs something to do in that down time between matches. That's where the pre-med classes come in.

At a panel discussion Wednesday, Williams explained that she's not necessarily interested in becoming a doctor, but wants to study nutrition, holistic medicine, and healing naturally.

"I love the holistic side of medicine," she said. Besides, she explained, during tournaments she actually has more free time than when she's not playing. "I like to keep going," she said. "I don't like to be still."

At the panel, part of the Fast Company Innovation Festival, Williams was interviewed along with Nike CEO Mike Parker, with whom she works closely. Asked what she'd be doing in 10 years, she quipped: "That's why Mark and I are so close. Because I'm going to be the CEO." The audience erupted in applause.

But Williams also made it clear that despite all her other activities, she's not any less motivated by tennis — even though she never thought she'd be still playing at age 30, let alone now at 34.

"I think it's really important to know what you're good at — and I know what I'm good at," she said. "For me right now ... I love being on the court, I love winning titles. So as much as these opportunities come up, and so many things come up, but is it going to interfere with my being the best in the world? If the answer is even close to yes, then I have to say no. I have the rest of my life to figure these things out."

Williams was also asked about the much-discussed incident where she chased down a thief who'd grabbed her cellphone in a restaurant. Asked what she was thinking when she chased the guy down, she said: "I wasn't, really."

"I just jumped up and I ran," she said, "and when I got there I thought, 'Oh, what am I doing, this could be it!'" But the thief, professing confusion, handed the phone back from under his sleeve. The next day, she said, her father called and said, 'Serena, if you need a phone, I'll buy you three or four phones! Just please don't do that again.'"

Naturally, Williams was also asked about her recent U.S. Open semifinal loss to Italy's Roberta Vinci, which derailed her quest for a Grand Slam. What happened, she was asked?

"I didn't win!" she said to laughter. "She played well. I don't think I played the best I could have ...but she played an outstanding match, and that happens sometimes. And unfortunately I didn't win but I did the best I could. It was what it was, and it was hard to put behind me, but I eventually did."

And, she added with a smile: "I can't wait to play her again!"