Former world number one Martina Navratilova is confident that Serena Williams will add more than 20 Grand Slam titles to her achievements.
The 32-year-old, who finished last season as WTA Championships winner, currently has 17 to her name - one fewer than Navratilova.
"If she can stay healthy, there is no doubt she can go into the 20s - the sky is the limit," BBC Sport quotes Navratilova as saying.
"I know how hard it is once you get to 30, all those little niggling injuries get worse and it's much easier to have an off day, but still, she is eager and winning is very contagious. Once you get really used to it, you don't want to let go of it."
Margaret Court holds the record of 24 titles.
