Former world number one Andy Roddick believes Serena Williams should be regarded in the same vein as Michael Jordan and Muhammad Ali as the greatest athlete of all time.

Serena Williams recently won the 2017 Australian Open, beating her sister Venus Williams 6-4, 6-4 to win the event for a record seventh time. In the process, she overtook Steffi Graf for most Grand Slam singles titles in the Open era with 23.

The 35-year-old, who took over as world number one from Angelique Kerber following the Australian Open, is now one major title away from tying Margaret Court's record of 24 Grand Slams, the most that any player has won in tennis history.

Roddick, a former US champion, told ESPN: "It's amazing. I've known Serena since we were 8 or 9 years old.

"To see her go from the girl I used to practice next to all the time to become this icon — and not just one of the greatest women athletes of all time, but one of the greatest athletes of all time, it's amazing.

"Watching her march her way through the history of our sport has been a pleasure. She's always been a friend first, and it's hard for me to disassociate that from who she has become, but it's been amazing to see.

When asked if Williams is the greatest of all time, Roddick responded that there were no doubts about that.

"I don't think it is a question. I think it is a matter of correcting rhetoric," he said. "Saying she's the best woman athlete shouldn't be taken as offensive as long as she's in the conversation with the greatest male athletes of all time as well.

"We need to enter her into the conversation with [Michael] Jordan and [Muhammad] Ali.

"I think that's where the respect lies, and where the conversation needs to go, after the acknowledgement of what she's done for women in sports."

Despite her age, Williams has shown no signs of slowing down. She didn't drop a single set in Melbourne, nor was she forced into a tie breaker.