Ashleigh Barty, the tennis world No 1, became the most significant name to drop out of a major as global Covid-19 surges sparked fresh concern that a host of international sports face more disruption.
The 24-year-old, who soared through the rankings last year by winning the French Open and three other singles titles, pulled out of next month's US Open, citing "still significant risks" for her reason to stay at home in Australia.
Her announcement came as concern was signalled in cycling over the likelihood of the Tour de France going ahead as planned. David Lappartient, the president of cycling’s world governing body the UCI, admitted that every race this season remains at risk of cancellation.
The comparatively successful returns of domestic football and cricket behind closed doors have distracted attention from evidence that sport remains blighted by uncertainty globally, with policies varying from country to country.
Prime Minister Boris Johnson warned this week there are signs of a "second wave" in Europe, and infection rates are rising again even more rapidly further afield. An increase of 10,000 Covid-19 deaths in 11 days in the United States is the fastest since early June.
In golf, Lee Westwood has become one the most prominent players to express concerns over travelling to the US, pulling out of the PGA Championship, now taking place at TPC Harding Park in San Francisco from Aug 6. With the 2020 Ryder Cup postponed and the majors badly hampered, Rory McIlroy had also said he "doesn't know" if he will compete in European events this year due to travel worries.
In tennis, after Wimbledon was cancelled, the withdrawal of Barty is a devastating blow for the US Open. "My team and I have decided that we won't be travelling to the US and Western and Southern Open and the US Open this year," Barty had said in a statement, and she is undecided on resuming her season in time for the French Open in Paris.
Her compatriot Nick Kyrgios has also suggested he will withdraw from events, having been critical of Novak Djokovic for catching the virus during his Adria tournament.
Snooker sees the return of spectators at the Crucible on Friday for the World Championship, but there will be no Anthony Hamilton, who has pulled in part due to his severe asthma.
With cases surging in Spain, a host of tournaments have been plunged into uncertainty. Uefa is ready to move the Women's Champions League quarter-finals venues should the new flurry of cases mean it is not safe to play.
In cycling, meanwhile, five riders have so far been forced to pull out of this week’s Vuelta a Burgos, where Belgian sensation Remco Evenepoel took victory in Thursday’s third stage.
Although the five did not test positive for Covid-19 themselves, they came into contact with people who did and were withdrawn by their respective teams Israel Start-Up Nation and UAE Team Emirates. The confusion led EF Pro Cycling manager Jonathan Vaughters to describe cycling’s return in Spain as a “mess”. On Wednesday, the UCI announced fines and other punishments for riders and race organisers who broke the protocols. “Every race is at risk, even the Tour," Lappartient told La Gazzetta dello Sport.
In domestic sport in America, MLS football matches have been postponed over positive tests among players, and a series of high-profile NFL and Major League Baseball stars have opted against starting the new season until further clarity is offered with rigid safety measures. Deaths from Covid-19 surpassed 150,000 in the United States on Wednesday, more than any other country.