Venus Williams has always taken her role as big sister to Serena very seriously but never before had she thought a bit of family intuition would end up saving the life of the 13-times Grand Slam champion.

Serena, who once starred in the American medical drama ER, found herself in the centre of her own health scare in February when she had to undergo emergency treatment after a life-threatening blood clot was found in one of her lungs.

Had it not been for a tip off from Venus, Serena may have been prevented from making her long-awaited comeback to competitive tennis this week in the Wimbledon warm-up tournament in the British seaside town of Eastbourne.

"I remember I was in the gym and Serena called me and said 'my foot's swelling'," Venus, who is celebrating her 31st birthday this week as she too makes a comeback, told Reuters in an interview.

"My physio and I were both there and I said 'you need to look up online on symptoms of blood clots'. So she did and our physio went back and what do you know, it was.

"She had lot of the symptoms and thank god she did not ignore it because that could have been dangerous.

"I wasn't with her so it wasn't like I could do anything... but I just suggested because it was one of the symptoms. I did not believe this could even happen to her."

Already known as a tennis champion, fashion designer and interior designer, Venus never thought her limited medical knowhow could prove so crucial.

"Someone like Serena, who's a champion and a legend and has spent her whole career and lifestyle being healthy, it's hard to expect her to have a health problem like she did," added five-times Wimbledon champion Venus, who is making her own comeback after missing six months with an abdominal injury.

"Everyone was surprised, including us.

"Thankfully we were able to recognise it and help her to get treatment right away. A lot of things you can think 'gosh, this is not really happening to me as I'm super healthy' and it can happen to anyone."

Like Serena, Venus also had to bide her time on the sidelines as she allowed her battered and bruised body to recover from a series of injuries that have limited her participation to just the Grand Slams over the past year.

This week, she seemed to lap up the atmosphere at the picturesque setting of Devonshire Park, where her face was plastered across dozens of billboards and hoardings dotted around the tennis complex.

Dressed in a white tracksuit over a bright pink tank top, she did not appear to have a care in the world as she strode purposefully into the ground's Champagne Bar area, only stopping once to sign a giant tennis ball for a young boy.

Venus, a keen historian of tennis, knows that no woman over 30 has won a Grand Slam trophy in over two decades.

But such a statistic does not concern the statuesque American, especially since recent trends show that those aged around 30 are most likely to succeed.

Over the past 13 months, Li Na and Francesca Schiavone have won French Open crowns aged 29, while 28-year-old Kim Clijsters is the U.S. and Australian Open champion and Serena, 29, is the Wimbledon holder.

"Tennis has changed a lot. People are now trying to be healthier and everyone's believing they can play longer. I think the days of retiring at 27 are over," explained Venus.

"By the time you get to the age I am, that's when you really start to understand the game and you can take advantage of that. So I'm going to stay and take advantage of all my experience."

Her vow to play on will strike fear into rivals, especially since the Williams sisters have ruled Wimbledon in nine of the past 11 years.

Critics have been laying into the women's game in recent weeks, saying it is suffering an identity crisis as the public at large can barely recognise any of the current top 10.

Should either of the Williams sisters triumph at Wimbledon on July 2 after barely playing any match for months, it will again raise questions about the strength of the women's tour.

Venus, however, dispelled suggestions that a Williams' victory will only highlight the poor state of the women's game.

"If we come back and play well, that's credit to our games. It's not easy to win majors because if it was, everyone would be doing it," said Venus, who expects a low seeding at the grass slam since injury means she is ranked outside the top 30.

"We have dropped ranking points and that's part of being off but at this point we're happy to be back, we're here to play, we're in the draw and that's what matters."