The 29-year-old Venus lost to Serena at Wimbledon this month, keeping her at five. Serena now has three Wimbledon crowns and is 15 months younger.
"They'll have to play a lot of years to catch up," Navratilova said in a phone interview. "Venus really needed to win this year. The closer you get to 30, the body starts slowing down. It doesn't obey as well."
On Wednesday night, Navratilova and the Boston Lobsters of World Team Tennis will face John McEnroe and the New York Sportimes in Manhattan.
The 52-year-old Navratilova is playing a record 20th season for World Team Tennis and is a commentator for The Tennis Channel.
Dudek wants Alonso reunionCanas beats Dimitrov in Swedish Open 1st round
