Serena Williams (Getty Images)
Rio de Janeiro - Steffi Graf says it is just a matter of time before a current star repeats her unique achievement of winning the four Grand Slams and Olympic gold in a single season.
As a 19-year-old, Graf made history by becoming the only player to win all four majors, plus Olympic gold, a feat dubbed the 'Golden Slam', when she beat Gabriela Sabatini in the final of the 1988 Seoul games.
Having retired in 1999, aged 30, with 22 Grand Slam titles to her name, Graf, now 47, is in Rio de Janeiro to see if Andy Murray and Serena Williams can defend the respective Olympic titles they won four years ago in London.
And, along with current world number one Novak Djokovic, she says the trio have the talent to one day repeat her golden sweep.
"I think someone will do it. There have been some outstanding athletes in recent years, like Novak Djokovic, Serena Williams and also Andy Murray," Germany's Graf told SID, an AFP subsidiary.
"I definitely think that there is someone who will do it again."
Graf, who is married to tennis legend Andre Agassi, says compatriot Angelique Kerber has a realistic chance of dethroning Williams in Rio to win the women's gold.
"It's hard to say. Serena is such an extraordinary athlete," said Graf after Kerber beat Williams in the Australian Open final, but lost to the American in the Wimbledon final.
"What she has achieved over such a long time is simply applaudable.
"It is physically and mentally tough in our sport, but I'll keep my fingers crossed.
"She (Kerber) has had a great year so far by winning the Australian Open and reaching the Wimbledon final.
"She has shown she is playing at a high level with a lot of confidence.
"I don't want to put too much pressure on her, but I have big hopes that she can win a medal."