Serena Williams has withdrawn from the WTA Finals due to persistent shoulder injuries.

The American world number two has been sidelined since the US Open, where she made the semi-finals despite a knee injury.

Williams, 35, announced she intended to once more skip the season-ending event in Singapore.

"I'm really, really bummed that I won't be able to come compete this year," Williams said via WTA.

"It's been a really tough year for me, just dealing so much with these shoulder injuries.

"My doctors insisted I stay home and heal it every single day, doing different treatments every day so I can have chance of playing next year and hopefully make Singapore. That will be my biggest goal. I have so much fun there. I only have wonderful memories playing in Singapore.

"I will really miss my fans most of all. Also just the atmosphere of being there. I do want to wish everyone a great time. I know it will be an amazing tournament, it always is. I really hope and look forward to seeing everyone next year."

The 22-time grand-slam champion also missed the WTA Finals last year, when her campaign came to an end after the US Open.