Serena Williams is unsure when she will make her grand slam return as the American said winning 25 majors was a goal.

Williams will make her competitive return on Sunday, scheduled to play doubles for the United States against Netherlands in the Fed Cup.

The 36-year-old last played competitively at the 2017 Australian Open, having given birth to her first child in September.

But it remains unclear when the 23-time major winner will again feature in a grand slam.

"Right now I'm focused on this weekend and after that I'll figure out what it might be," Williams said on Friday after adding she was unsure if she would play the French Open starting in May.

Williams' success in Melbourne last year marked her 23rd grand slam, leaving her second only to Margaret Court (24) for most major titles.

Overtaking Court remains a goal for Williams, who would like to go even further than 25 grand slams.

"I have long-term goals obviously, but right now my main goal is just to stay in the moment," she said.

"It goes unsaid 25 is obviously something that I would love, but I hate to limit myself."