Serena Williams is setting her sights on more titles as she returns to action in Madrid after saying she needed a "break" following an opening-round exit at Charleston four weeks ago.

"I feel pressure every day. I think it’s a good thing a little bit because it means I’m still really hungry. If I didn’t, then I would be like, 'Oh, it doesn’t matter,'” she said in an interview to promote the Madrid tournament.

The world No. 1 said she and her sister, Venus, also want to continue having an impact off the court. Serena was one of five athletes and the only tennis player to be named one of TIME magazine's 100 Most Influential People of the year last week.

''If Venus and I ever looked at each other and reflected on what we did, we wouldn’t be here. We would be vacationing on some exotic island somewhere," she said. "We can’t become satisfied yet, because there are still some things that we want to do. I think there’s some pioneering to be done. Obviously, Venus has done some pioneering of her own with everything that she’s done for equal prize money and things of that nature, so I definitely think there’s still lots of room. We’ve opened so many doors, I have to think about what next steps are."

In Charleston, Serena said that she was feeling the effects of playing a heavy schedule the past two years.

"I need some weeks off where I don't think about tennis and kind of regroup," Williams said.

Williams, who lives in Floria, was photographed relaxing on Miami Beach two weeks ago and resumed training at the Mouratoglou academy last week.