LAUSANNE, Switzerland—After five weeks of concern about the safety of tennis player Peng Shuai in China, the International Olympic Committee (IOC) said Tuesday it cannot give any certainties about her case. The IOC’s two video calls with the Grand Slam doubles champion are the only reported contacts Peng has had with people outside China since November 2 when she sent a social media post alleging she was sexually assaulted by a former top Communist Party official. Critics have claimed the IOC is enabling a cover-up by China ahead of the state-backed project to host the Winter Olympics in Beiji…