A grateful Serena Williams realizes just how close she came to losing her tennis career because of blood clots in both lungs.

"A lot of people die from that because you don't recognize it," the 13-time Grand Slam champion said Monday, a day before returning to action at the Eastbourne International after nearly a year away from competition.

"They (the doctors) just said it could have gotten a lot more serious a day later or two days later. It could have possibly been career-ending, but for the grace of God I got there in time and I was able to recover from it."

The 29-year-old Williams' travails all started at a night out at a restaurant shortly after she won her fourth Wimbledon title last summer. Wearing sandals instead of boots to show off a new pedicure, Williams stepped on broken glass.

"My coach, he took his phone, he looked down and there's like this massive puddle of blood. I was like, 'Oh, my gosh,'" she said. "I ended up fainting because I lost so much blood."

The ligament damage to her foot required two bouts of surgery, 10 weeks in plaster and 10 weeks in a protective boot.

"I was debating whether I'd rather be in jail for 20 weeks or a cast, and I was leaning towards jail because I really hated that cast," she said. "Mentally that was one of the toughest things for me."

But then in February, she had trouble breathing.

"I always use the word 'blessed.' I had great people around me," she said. "My (trainer) forced me to go to the hospital, whereas I was actually on the way to a party, to be quite honest. She's like, 'No, you need to go to the hospital.'

"Glad I didn't go to that party."

Finally fit, she joined sister Venus in entering Eastbourne, breaking with their normal tradition of preparing for Wimbledon at home in Florida. Serena's statement last week confirming her long-awaited return ended with the words: "Serena's back!"

She was immediately installed as one of the favorites for Wimbledon, despite her lack of preparation.

Women's tennis has struggled to fill the void left by the sisters. In Serena's absence, Caroline Wozniacki has taken the No. 1 ranking, but the 20-year-old Dane has struggled to justify that status without a grand slam title to her name. Compelling rivalries and story lines are lacking.

"We've missed tennis so much," Serena said. "If tennis has missed us half as much as we have missed tennis, we're in a good place."

Venus returned with a three-set win over eighth-seeded Andrea Petkovic on Monday. Serena looks to follow her sister into the second round when she faces Tsvetana Pironkova of Bulgaria on Tuesday.

The younger sister is adamant that while the experience of a potentially career-ending illness means she's no longer "taking things for granted," she isn't coming back to play for fun.

"My attitude hasn't changed. I still cracked a couple of rackets in practice," she said. "But that's good. That just still makes me feel like I have that desire, and I have that insatiable, just innate thing inside me that I just want everything and I just want to win."

Williams wouldn't say whether winning a fifth Wimbledon title in three weeks' time was a realistic aim, although she is hoping to peak in the second week and take it from there.

"I'm not preparing for today or Wimbledon," she said. "I'm preparing for the rest of my career."