A "viral illness" was the official prognosis to explain Williams' disoriented state on the court during her second-round doubles match on Tuesday, but there is conjecture amongst those in the tennis scene there might be more to the story than first thought.

Navratilova, a nine-time Wimbledon singles champion, said she cannot understand how Williams was even allowed on the court given her poor physical state.

"I find it distressing," Navratilova told ESPN. "I think virus, whatever they're saying it was, I don't think that was it. I think it's clear that's not the case. I don't know what it is, but I hope Serena will be OK. And most of all, I don't know how she ended up walking onto the court.

"It's the most inexplicable thing of all that she was clearly in no state to play a match and that with all the people around her, that they didn't stop her from getting on the court," Navratilova said.

Williams struggled to catch balls, make contact or even toss a ball in warm ups. The match was delayed for 13 minutes while Williams was attended to by medical staff by her sister's side.

When proceedings finally got under way Williams was lethargic, dispirited and subsequently served eight consecutive service faults in the third game of the match which prompted chair umpire to Kader Nouni to get off his chair and see if the 32-year-old was fit to continue.

After the match, Williams posted a bed-ridden photo of herself on Instagram hours after the incident.

Navratilova's suspicions began to rise when Williams' coach, Patrick Mouratoglou, said he had not seen Serena for two days before the match.

"Everybody was put in such a difficult position, including the WTA, it's not right," Navratilova said. "It defies logic on so many fronts. The coach said he hadn't seen her for two days. He didn't know anything. How can you be a coach and not know anything? That's wrong. And Venus was just kind of there. You don't know what's going on, but virus was not it, that much is clear."

Williams, winner of 17 Grand Slams all up, was beaten on Saturday in the third round of singles by world No.25 Alize Cornet.

Navratilova said she sympathises with tennis players who want to be alone after a disappointing loss, but criticised Williams for turning the whole situation into a circus.

"Either you go home or default, I would expect a default before you play," Navratilova said. "But once you step onto the court, you're a professional tennis player, you've got to be ready to play. No matter what is ailing you or no matter if you did anything to get you in that state or you're sick or whatever, you don't step on the court. You don't step on the court no matter what."