Serena Williams' return to competitive tennis at Queen's Club has been overshadowed by concerns over the fitness of her doubles partner, Victoria Mboko, after the Canadian teenager suffered a knee injury during her singles match on Wednesday.
Williams, 44, made her long-awaited comeback on Tuesday after nearly four years away from the sport, teaming up with the 19-year-old Mboko in the doubles draw. The pair impressed on their debut, upsetting the third seeds to book a place in the quarter-finals.
However, their campaign is now under threat after Mboko was forced to retire from her singles match against Karolina Pliskova following a painful fall.
The incident occurred as Mboko stretched to retrieve a forehand from the Czech, who was facing break point. She slipped on the grass and collapsed clutching her left knee, immediately crying out in pain.
Although Mboko managed to get back to her feet and return to her chair, she was visibly distressed. The teenager covered her face with a towel before retiring from the match and limping off court in tears.
"It's such a shame," said Pliskova, who was leading 6-2, 3-4 when the match ended. "I think we played quite a good match and she was improving as it went on. I wish her only the best. It's not the way I want to win, so hopefully she is going to be fine for Wimbledon."
Mboko and Williams are scheduled to face Canada's Leylah Fernandez and Germany's Laura Siegemund in Thursday's quarter-final, but her participation now appears uncertain.
Former British number one Annabel Croft described the injury as a worrying setback.
"It's a heartbreaker. You hate to see that," Croft said on BBC Two. "She would have been so excited to continue playing alongside Serena.
"It's a classic grass-court injury, where the legs go in different directions and the knee twists. You just hope and pray she's not ruled out of Wimbledon."
Wimbledon, the season's only Grand Slam played on grass, begins on 29 June, leaving little time for recovery should the injury prove serious.
"She's absolutely devastated," Croft added. "And it's devastating for fans too, because she's one of the brightest young talents in the game and has been making such impressive progress on tour."
