Tennis is facing an existential crisis over doping. How will it respond?

As the Australian Open gets under way in Melbourne, the sport is facing a crisis over positive doping tests involving two of the biggest stars in tennis.

Last March, the top-ranked men's player, Jannik Sinner, tested positive for clostebol, a banned anabolic agent, twice. The substance was quickly traced to a product that was used to treat a cut on the hand of Sinner's physiotherapist.

The International Te