Andy Murray believes Serena Williams can return to win Grand Slam titles after she gives birth to her first child this fall.

That's because the world No. 1 regards Serena as "probably the greatest tennis player ever."

Watch: Serena Pregnant, Plans Comeback

The 23-time Grand Slam champion, who is engaged to Reddit co-founder Alexis Ohanian, announced she is 20 weeks pregnant and expects to give birth in September.

Asked if he believes the Australian Open champion can win majors after becoming a mom, Murray said he doesn't doubt Williams.

"Yeah, I mean, why not? Obviously I'd imagine it's difficult and will take a lot of hard work," Murray told the media in Monte Carlo. "But I think if the desire is there to do it, she's obviously an incredible athlete, probably the greatest tennis player ever. Yeah, I mean, if anyone can, I'd imagine it would be her.

"Just depends how much she wants to do it."

Photo credit: Reuters