Serena Williams' comeback campaign has hit an early hurdle after her doubles partner, Victoria Mboko, was forced to retire from her opening singles match at theHSBC Championshipsin London.

The 19-year-old Canadian had admitted before the tournament that grass was not her strongest surface, only to suffer a left knee injury on that same court just days later.

'I'm not very good on the grass,' Mboko said before the event. 'It's a little bit tough changing surfaces on the body, but I like doing challenges and I like things that come new to me,' she added.

Mboko, who received a bye into the last 16, was down a set but leading Karolina Pliskova 4-3 in the second when disaster struck. Chasing down a shot behind the baseline, she slipped and was forced into the splits, drawing an audible gasp from the crowd.

Though visibly distressed, Mboko managed to get back to her feet and walk under her own power to the bench. Hiding her face behind a towel, she consulted with her team before the umpire eventually announced her retirement from the match. The crowd responded with a warm round of applause as she left the court.

Williams and Mboko have hit together only once since their partnership was publicly confirmed. The pair made their doubles debut on Tuesday, securing a first-round victory over Nicole Melichar-Martinez and Erin Routliffe at the HSBC Championships, hosted by The Queen's Club.

Williams, 44, accepted a wild card to compete at The Queen's Club grass-court tournament after announcing in 2022 that she was 'evolving' away from competitive tennis. Her last competitive match came at the 2022 US Open.

Williams is also scheduled to play doubles at theBerlin Tennis Openlater this month, although her partner for that event has yet to be announced.

Mboko was in France last month when she received a notification from someone 'maybe' named 'Serena'. Indeed it was, and Williams asked Mboko if she would be her doubles partner.

'How could I decline that?' Mboko said in an exclusive interview on Friday withCBC Sportshost Anastasia Bucsis.

Source: International Business Times UK