Serena Williams is "not obsessed" with equalling the record of 24 Grand Slam singles titles but still wants to win, says her coach Patrick Mouratoglou.

Williams' last major came at Melbourne Park while she was pregnant in 2017.

"Does she need that validation? I don't think she needs that validation," said Mouratoglou about chasing a 24th title.

Australian Court set a record that straddled the amateur and Open eras, with 13 of her victories coming in the pre-professional age before 1968.

Williams, whose daughter Olympia is now three years old, has lost four finals since her last victory in a Grand Slam, including against Halep at Wimbledon in 2019.

"Clearly she came back to tennis to win some other Grand Slams, so that's for sure the goal," added Mouratoglou.

"Now, she's not as obsessed with the 24 than most of the people in the tennis world, but definitely she wants to win Grand Slams.

"There is tennis before the Open era and tennis after the Open era. We all know it's two different sports. It's an amateur sport and a professional sport. It doesn't really make sense to compare."

'Wimbledon final was best day of my life'

Williams leads their head-to-head record 9-2 but Halep produced one of the great recent Grand Slam performances to win that Wimbledon final two years ago.

"The game, I think it was one of the best in my life," said the Romanian. "The best day of my life. I felt very confident back then. I felt every ball.

"We played so many times. I know what to expect. I will just try to do my game, and I will be confident."

Japan's Naomi Osaka is also in action on Tuesday against Hsieh Su-wei, who at 35 became the oldest player to reach a first Slam quarter-final in the Open era.

"She's one of those players that, for me, if it was a video game, I would want to select her character just to play as her," said 2019 champion Osaka.

"Because my mind can't fathom the choices she makes when she's on the court. It's so fun to watch. It's not fun to play against, but it's really fun to watch."