Novak Djokovic’s hopes of competing for his 21st grand slam singles title at the Australian Open this month is in danger of being crushed as he was held at an airport amid outcry over his controversial “medical exemption” from getting vaccinated agreed by the tournament’s organizers. The world No. 1 and reigning Australian Open champion was held up at passport control at Tullamarine airport in Melbourne, the host city of the tournament, for several hours late at night as he was questioned.