(Reuters) – Serena Williams has withdrawn from the season-ending WTA Finals in Singapore later this month citing a persistent shoulder injury, the world number two said on Monday.

The 22-times grand slam singles champion has played only eight tournaments this year and lost her top rankings to German Angelique Kerber.

“It’s been a really tough year for me, dealing with these shoulder injuries. My doctor insists that I stay home and heal it. I only have wonderful memories of playing in Singapore and I will really miss my fans,” the 35-year-old said in a video on the WTA website.

Williams, who also missed Wuhan Open and China Open and a tournament in Cincinnati this year, added that she will be “off

court for the next several weeks”.

The American arrived at the year’s U.S Open with concerns around a sore shoulder from the Rio Olympics in August and was beaten by Czech 10th seed Karolina Pliskova in the semi-final at the Flushing Meadows.

Williams, who had also pulled out of last year’s WTA Finals, has won two titles this year, in Rome and at Wimbledon, where she matched Steffi Graf’s professional era record of 22 grand slam singles titles.

Kerber, Simona Halep, Agnieszka Radwanska, Karolina Pliskova and Garbine Muguruza, Madison Keys and Dominika Cibulkova have already qualified for the WTA Finals starting on Sunday.

(Reporting by Ian Rodricks in Bengaluru; editing by Amlan Chakraborty)