Roger Federer is set to play at the Madrid Open next month, but Serena Williams will not compete following controversial comments from tournament director Ion Tiriac earlier this year.
Federer, 39, made his long-awaited return after 13 months out in Doha, but has not played since.
He has said the grass is the "beginning of the season" for him as he looks to get back to full fitness, but he will play Madrid for only the second time since 2015.
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World No 1 Novak Djokovic is also set to play along with five-time champion Rafael Nadal.
Madrid was not played last year due to the Covid-19 pandemic and if Federer, Djokovic and Nadal all compete it will be the first time they have all played the same tournament since the 2020 Australian Open.
Along with the ‘Big Three’, all of the top 45 players in the ATP rankings are signed up for the tournament, which runs from May 2-9. However, the list is subject to change and it has been reported in Serbia that Djokovic may not play.
The women’s field is just as high-quality with world No 1 Ashleigh Barty, Australian Open champion Naomi Osaka and Simona Halep set to play.
Barty and Osaka both made the quarter-finals in 2019 while Halep is a two-time champion and finished as runner-up to Kiki Bertens last time out.
Williams will not be in attendance though.
The 23-time Grand Slam champion was criticised earlier this year by tournament director Tiriac, who said if "she had a little decency, she would retire".
The comments were condemned by Williams’ husband Alexis Ohanian Sr, among others. He wrote on Twitter: "Safe to say no one gives a damn what Ion Țiriac thinks...2021 and no holding back when a racist/sexist clown with a platform comes for my family."

How will Federer's clay season pan out?

Federer’s return to Madrid is the first sign of his plan for the clay season.
He was originally set to play in Dubai following his comeback in Doha but pulled out of that tournament, so hasn’t played a competitive match since March 11. If he doesn’t play again until Madrid that will be two months without an appearance at a tournament.
He will not be playing in the first clay Masters 1000 of the season in Monte Carlo next week, where Nadal and Djokovic are expected to return, but will he look to get some match practice in the subsequent weeks before heading to Madrid?
After losing in Doha he said that he thinks “matches are important” as he looks to recover his best form ahead of his main objectives on grass in the summer.

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“What comes before the grass courts are the clay courts. So from that standpoint, I have no choice but to play on clay if I want to play matches.
“It could be good for me, the clay. It could be bad for me. So I will only know in practice, but I don’t think it’s going to be bad, to be honest. I assume I will play some clay. The question is what… Everything is geared towards the grass. So whatever makes me be 100 per cent there, I will do.”
If he does return to action in Madrid then perhaps his next port of call will be his home country of Switzerland to play in the Geneva Open on May 16. Roland-Garros is then set to start on May 23 before attentions turn to the grass.
It will be intriguing to see how Federer’s plans develop over the next few months. He had cut down on his clay schedule before injury last year, playing at just one of the last five French Opens and not winning a clay title since 2015. But his situation may require him to get back on the dirt more than expected before he takes on the grass.

Where next for Serena?

While Federer's plan is starting to take shape, there's still uncertainty over what Williams will do next.
She hasn't played since an emotional exit at the Australian Open, having missed the Miami Open after oral surgery.
Like Federer she has cut down on her clay appearances in the last few years, only playing in one other clay tournament outside of Roland-Garros since making the final in Paris in 2016.
It would not be a huge surprise to see Williams skip most of the clay season, including perhaps Roland-Garros, but how that would impact her preparations for the summer and a potential tilt at Wimbledon and the Olympics is unclear.

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