LIMELETTE, Belgium -- The determination that helped Justine Henin beat bigger, stronger opponents time and again was fading.

"I decided," Henin said, "to stop fooling myself and accept it."

Henin retired from tennis Wednesday at age 25, an abrupt ending to a career in which she won seven Grand Slam singles titles and spent more than 100 weeks ranked No. 1.

She announced her decision at a news conference one and a half weeks before the start of the French Open, where she had won the past three titles and four overall.

Put simply, she realized she was burned out, and became the first woman to quit the sport while atop the WTA rankings.

"I always based everything on this motivation -- this flame -- that was in me. And once I lost that, I lost many, many things," Henin said.

Her agent, Ken Meyerson, told ESPN.com's Bonnie D. Ford that Henin called him Sunday evening and, in what he described as a "warm" conversation, said, "I've won everything I need to win, I have more money than I can use in three lifetimes, and I don't have the will to play one day more."

Henin told Meyerson she had been thinking about the decision for five or six months. Her play over that period has been flat, partly because of a troublesome knee that required cortisone treatment, but Meyerson said the reasoning behind her retirement is all emotional.

"She's simply burned out and has no more juice to go on," Meyerson told ESPN.com.

Justine Henin consoles her coach, Carlos Rodriguez, right, at her news conference announcing her retirement on Wednesday. Dominique Faget/AFP/Getty Images

"I was surprised at the urgency of the decision. We, as agents, like long farewells. I'm really sad," he said. "She did so much for the game, and we need her in the women's game. Pound-for-pound, she was one of the best tennis players in history. She was an underdog. She was someone we could relate to."

Surprising as her departure was to the rest of the world, it seemed somehow inevitable to her.

After reaching the final at each Grand Slam tournament in 2006, she won 10 tournaments in 2007, including two majors. But this season, she started to find it an ever bigger chore to pack her luggage to travel to tournaments. Her legs felt heavy when she should have been dancing in the backcourt, ready to turn another one of those sparkling backhands into a winner.