It's been another tough year for Naomi Osaka, who has not won a tennis tournament since the Australian Open in 2021.

The former world number one has struggled with multiple injuries over the last 18 months and she has suffered a number of early tournament defeats.

Since claiming her fourth Grand Slam title, fans have only seen glimpses of Osaka's full potential. But Pam Shriver has a little nugget of advice to hopefully get her back to the world-beating form she has produced in the past.

What did Pam Shriver say?

Shriver, who partnered Martina Navratilova during a hugely successful doubles career, has discussed Osaka's recent struggles and refuses to rule out the 24-year-old returning to greatness.

Osaka was left disappointed when Danielle Collins knocked her out of the first round of the US Open earlier this month. This marked Osaka's third consecutive first round exit, after previously withdrawing from the Canadian Open due to injury and falling to Zhang Shuai at the Cincinnati Masters.

"Listen, it was a tough draw to play Collins [in the] first round," Shriver said on Tennis Channel's Inside-In podcast (h/t Sportskeeda). "Naomi didn't play badly and I was texting Stuart, her business partner like, 'you gotta play more!', and it's like, 'okay but she has to want to play more.'

"I'd like to see her play a couple more tournaments before the end of the year. Naomi might learn a little bit."

LOS ANGELES, CA - OCTOBER 01: Former professional tennis player Pam Shriver attends 'Creating Change Through Sports' hosted by Up2Us on October 1, 2013 in Los Angeles, California. 'Creating Change Through Sports' sends 150 coaches to mentor 15,000 youth in underserved communities. (Photo by Imeh Akpanudosen/Getty Images for Up2Us)

Osaka has played in just 11 tournaments this year. While she did reach the final of the Miami Open in April, this was her best tournament result since the 2021 Australian Open.

The Japanese star also faced a hefty drop down the world rankings after she failed to defend her title in Melbourne this January.

Osaka plummeted from 14th in the world to 85th, but over the months she has been able to steadily climb her way into the top 50.

PARIS, FRANCE - MAY 23: Naomi Osaka of Japan celebrates against Amanda Anisimova of USA during the Women's Singles First Round match on Day 2 of The 2022 French Open at Roland Garros on May 23, 2022 in Paris, France. (Photo by Ryan Pierse/Getty Images)

Shriver compared the world number 46's struggles to Serena Williams, and has encouraged Osaka to get herself out on the court more.

"When I think back to how Serena was able to win the 2007 Australian Open — outside the top 70, unseeded, out of shape, hadn't played any matches, and then worked her way into form.

"Really, the best way to do that is just to play matches. You get sparks of motivation by seeing glimpses of your best self and then that makes you want to go out and work harder."

CINCINNATI, OH - AUGUST 17: Serena Williams appears on the ESPN Game Day desk with Pam Shriver after her win over Na Li of China during the semifinals of the Western & Southern Open on August 17, 2013 at Lindner Family Tennis Center in Cincinnati, Ohio. Williams was presented a trophy for clinching the Emirites Airlines US Open Series with the win. (Photo by Matthew Stockman/Getty Images)

What happened to Naomi Osaka?

After winning her fourth Grand Slam in as many years at the 2021 Australian Open, it looked like the only way was up for Osaka.

However, last year was a serious challenge for the former world number one.

During the French Open, Osaka revealed she had been suffering from bouts of depression and anxiety after opting to boycott media duties.

Her reason was to highlight how certain angles of questioning can often impact the mental wellbeing of athletes. Osaka herself has been reduced to tears during a press conference before.

When Roland-Garros threatened Osaka with expulsion and a fine for her boycott, she withdrew from the tournament and took a break from tennis.

MADRID, SPAIN - MAY 01: Naomi Osaka of Japan plays a forehand against against Sara Sorribes Tormo of Spain during their Round of 32 match on Day Four of the Mutua Madrid Open at La Caja Magica on May 01, 2022 in Madrid, Spain. (Photo by Clive Brunskill/Getty Images)

She returned for the Tokyo Olympics and the US Open but then took another hiatus, disclosing that winning didn't make her happy anymore.

Osaka took a four-month break from tennis before making her comeback at the Melbourne Open this January.

Since her return, she has struggled with several injuries and most recently withdrew from the Pan Pacific Open with stomach problems. Osaka later announced in a statement that she would not be competing in any more tournaments this year.