Reese Witherspoon producing documentary about lesbian icon Martina Navratilova

Tennis player Martina Navratilova

Reese Witherspoon is producing a documentary about out tennis legend Martina Navratilova.

Navratilova, a beloved former tennis world number one, was one of the first out players at the top of a major sport, coming out in 1981.

The retired Czech-American player and LGBT rights pioneer, now 61, married longtime girlfriend Julia Lemigova in 2014 after proposing at the US Open.

The player will be the subject of a new documentary film produced by Legally Blonde star Reese Witherspoon.

Martina Navratilova of the United States stretches to make a back hand return during her Women’s Singles match against Helena Sukova at the US Open Tennis Championship on 4 September 1993 (Simon Bruty/Getty)

Witherspoon’s production company Hello Sunshine is developing the doc from out Pulitzer Prize-winning journalist Glenn Greenwald and Suzanne Gilbert.

Variety reports the film will explore Navratilova’s achievements and legacy as a social justice pioneer, through Greenwald’s “personal lens as a gay child growing up in Reagan-era Florida.”

Charlotte Koh, head of digital media and programming for Hello Sunshine: “The issues raised by Martina’s legacy resonate now more than ever, which is why it’s so important to tell her story to new generations of engaged young people who may not be aware of the vital role she played in shaping expectations around female identity and LGBT equality.

“Having producers Glenn and Suzanne reframe Martina’s impact on society through the lens of Glenn’s personal coming-of-age journey creates a fresh, intimate, and relatable film for a wide audience.”

Martina Navratilova of the United States during the Women’s Singles Semi Final match against Chris Evert at the French Open Tennis Championship on 5 June 1987 at the Stade Roland Garros in Paris, France. (Trevor Jones/Getty)

Greenwald added: “As monumental as Martina’s on-court achievements were, they pale in comparison to her role as a pioneer and trailblazer on questions of feminism, women’s athletics, equality for gay and lesbians across the planet, transgender visibility, immigrant rights, and the right of political dissent.

“I’m excited to be partnering with Reese and Hello Sunshine to explore her truly enduring legacy, her remarkable courage directly or indirectly inspiring millions of people who lacked any other role models.”

Greenwald won a Pulitzer in 2014 for reporting on the Edward Snowden leaks. He now writes for The Intercept, where is known for frequently-critical coverage of the Mueller investigation of Donald Trump.

Tennis player Martina Navratilova speak onstage at the FORTUNE Most Powerful Women Summit (Paul Morigi/Getty Images for FORTUNE)

Navratilova has been outspoken on LGBT rights for decades – speaking out about Russia’s anti-gay laws, calling out religious homophobia, and advocating for same-sex partnership rights.

She has also spoken about how disappointed she is that there are so few out male tennis players despite a number in the female sport.

Navratilova said recently: “On the tennis court, I would certainly like to see more players come out.

“I can’t believe that there has never been a male player that has taken that step.

“With each passing celebrity coming out or athlete, it becomes less of a big deal and that’s eventually what we want it to be, for it not just to matter.”

She continued: “It’s more difficult when you play team sports than when you play individual sports. As a tennis player, I could always play tennis.

“Nobody could tell me, no, you can’t play because; but in team sports, it’s more difficult.

“And of course it depends what country you’re in, because we still have countries where homosexuality is punishable by death, so we are talking about different situations here.

“In America we are fighting for equal rights and for the right to marry. In other countries, people are fighting for the right to stay alive.

“So it’s a different situation and it’s very individual, as is the decision to come out or not.”