Alexander Zverev’s bid for back-to-back Olympic gold could be under threat in connection with a knee injury he has sustained at Wimbledon, his brother has said. Mischa Zverev told Prime Video that 40 millilitres of liquid and blood were removed from the damaged left knee on Tuesday in London. He said Alexander Zverev will undergo another examination on Wednesday in Monaco to determine whether the injury is severe after all. “If it’s a fracture in the bone or a hairline fracture or whatever, then you have to see how long it lasts. But then the Olympics are in danger,” Mischa Zverev said. The Pa…