Australian tennis star Nick Kyrgios once said he could not stand Novak Djokovic, describing him as “a tool.” Yet, he has now become one of his old foe’s most unlikely and sympathetic backers, declaring that Djokovic hasn’t been treated humanely and that tennis really needs its world No.1 back at the Australian Open. As Djokovic underwent another night at the immigration detention hotel In Melbourne preparing for Monday’s legal hearing over whether he can stay in Australia and defend his title, he’ll doubtless have been touched, and a touch amazed, to hear of his unexpected new champion. Back home in Serbia on Saturday, Djokovic’s family held a rally in support of him in Belgrade for the third successive day while Prime Minister Ana Brnabic promised him the full weight of government support over his visa battle to ensure he could enter Australia. “We’ve managed to make sure gluten-free food is delivered …