LONDON, United Kingdom (AFP) — Serena Williams’s long-awaited return to competitive tennis was left in the balance Wednesday after doubles partner Victoria Mboko retired through injury in her opening singles match during the WTA tour event at Queen’s Club.

Tennis great Williams, 44, made her eagerly-anticipated comeback at the London venue on Tuesday, securing a win alongside Canadian teenager Mboko in their first doubles match.

The duo defeated third seeds Nicole Melichar-Martinez and Erin Routliffe 7-6 (7/2), 6-2.

They are now scheduled to face Leylah Fernandez and Laura Siegemund on Thursday in the grass-court event, a warm-up for Wimbledon.

Mboko, who received a bye into the round of 16 for the Queen’s singles, was down a set but leading Karolina Pliskova 4-3 in the second when she slipped behind the baseline trying to return a shot.

The stumble effectively forced her into doing the splits, drawing a gasp from the crowd.

Mboko was visibly upset as she spoke to the attending medical staff.

She got to her feet but the official reason subsequently given for her retirement was a left knee injury, with Mboko heard saying on television cameras “there is no stability right now.”

Mboko buried her face behind a towel as she continued to consult her team, before the umpire eventually announced her retirement, with the crowd giving the 19-year-old a sympathetic reception.

“It’s such a shame,” said Pliskova, adding: “Of course, this is not the way we want to win. Hopefully she is going to be fine for Wimbledon.”

If Mboko, ninth in the women’s singles rankings, withdraws from the doubles, that will be the end of Williams’s tournament as well.

Williams, a 23-time Grand Slam singles champion, stunned the sporting world a week ago with her shock announcement she would compete at Queen’s, where she is only playing in the doubles.

“It was so fun. I had so much fun playing with Victoria,” she said after Tuesday’s win.

Williams said her decision to return to competitive tennis for the first time since losing to Ajla Tomljanovic at the 2022 US Open was inspired by a desire to play in front of her children.

Her two young daughters, Olympia and Adira, as well as husband Alexis Ohanian were all courtside at Queen’s on Tuesday.

Williams is also scheduled to play doubles at the Berlin Open next week but has yet to decide if she wants to feature in the Wimbledon doubles.

But she played down the prospect of featuring in the singles at Wimbledon — where she has won the title seven times — when she faced the media on Sunday.