Serena Williams’ most recent official match did not end well — unless you were a Roberta Vinci fan — as Williams crashed out of last year’s US Open in the semifinals without completing the Grand Slam. Four months later, reassurance remains elusive, but with the Australian Open set to begin on Monday, Williams’ coach, Patrick Mouratoglou, said he was “confident Serena will be ready.”

After that shocking September defeat to Vinci, Williams ended her season to heal physically and psychologically, but at 34, she has struggled since her return.

She looked rusty when she played in the International Premier Tennis League last month in Manila, and then, visibly hampered by knee pain, she made a brief appearance at the Hopman Cup team event last week in Perth, Australia, before withdrawing.

Williams’ early-season form is typically difficult to read. Vulnerability does not necessarily mean big trouble, but she definitely appears vulnerable as she prepares to defend her Australian Open title.

Mouratoglou said Williams received a special treatment on her knees “once every six months.”

“She’s in very good health,” he said in French. “Her knees simply responded badly to a treatment that she received a few days before the Hopman Cup, and she experienced swelling. These are things that happen sometimes. It’s nothing to be concerned about, but she had to take an extra week of rest so that the swelling she could go away. It has now cleared up, and we can prepare as we would wish to for the Australian Open.”

Mouratoglou has compared Williams’ knee problems to those of the Spanish star Rafael Nadal, who has dealt with acute tendinitis. Nadal has missed significant stretches of play during his career, but Mouratoglou said his own comments on the issue had been misunderstood.

“I never said that the two players’ knees were in the same condition,” Mouratoglou said. “I simply underscored the fact that in both cases, they suffer from wear. Serena’s knees are doing very well if you consider that they are the knees of a 34-year-old professional player. They just need special attention. I don’t think they will be an obstacle to her performances in the future.”

What is clear is that Williams has become less certain to finish what she starts. In the past year, she has retired or withdrawn in the midst of four events, not including the mandatory WTA tournaments in Beijing and Singapore that she skipped at the end of 2015.

It was a meek finish to a big, bold season in which she won five singles titles, including the first three Grand Slam tournaments to run her career total to 21 — one short of Steffi Graf’s Open-era record of 22 and three short of Margaret Court’s career record of 24.

But it was not a dominant season in the classic sense. Williams was routinely pushed to three sets in the major tournaments and won the French Open despite illness and wildly fluctuating form.

In an interview at the end of last season, the veteran coach Wim Fissette, now working with Victoria Azarenka, expressed scepticism that Williams could replicate her formidable season in 2016.

“This was her year,” he said of 2015. “And I really don’t think she can do the same next year.”

Fissette acknowledged that even when Williams was playing “70 to 80 percent of her best level” in 2015, she was still able to beat anyone in the field.

“But to do that mentally and be ready to fight again for seven rounds in a Grand Slam and to stay fit between those tournaments — because more and more she’s just focusing on the Grand Slams — it still costs you a lot of energy and mental toughness,” he said. “I think it will be difficult for her to do that in 2016, but, well, Serena remains Serena. She’s a great champion, and maybe she will surprise me there again.”

Through the decades, counting out Williams has hardly been a winning strategy. But at some point, perhaps sooner rather than later, time will defeat her. She is already by far the oldest No 1 in the history of the WTA rankings.

“I think the Graf record will help her a lot in being motivated,” said Pam Shriver, an ESPN analyst and a former top player. “I think she wants to get to and pass her, and there’s also the Olympics, where her record is amazing. So I think in 2016 she will be motivated. So the question is, can she stay healthy?”

The other question is whether her would-be rivals will truly step up.
“I think 2016 is a huge year for people other than Serena to prove that they have what it takes,” Shriver said. “Who can think big enough to grasp the biggest trophies on the biggest stage? And in an Olympic year, it has that added pressure. We know Serena can do it, but if people were to look back on last year, they could say, ‘Was Serena’s tennis really good enough to win three majors and come within two matches of winning a Grand Slam?’”

Mouratoglou, who has coached Williams since June 2012, recommended against her playing in the final stretch of the 2015 season, in part because he wanted her to recover her motivation after the deflation of the Vinci upset.

“She has totally recovered from that defeat,” he said.
“Time allows you to put things in perspective and to realise what you’ve accomplished. She has won four of the last five Grand Slam tournaments. She lost three matches total in 2015 and finished No 1 for the third year in a row. I know she is again totally focused on her goals, because she is again working on continuing to evolve her game.”

Mouratoglou said the initial plan was to do pre-season training at his new academy in southern France, near Antibes. Novak Djokovic trained there in December. “It would have been fantastic because we would have seen the two world No 1s preparing for 2016 side by side,” Mouratoglou said.But Williams changed her plans for personal reasons, Mouratoglou said, and he spent three weeks in Florida with her instead.

“You can’t rest on your laurels,” he said. “If Serena has this margin over the others, it’s precisely because she is always working with this desire to progress and to add new things to her game. We worked in this direction during the pre-season.”