Four days before the start of the Australian Open, Olympic champion Alexander Zverev trained with German basketball great Dirk Nowitzki at the Melbourne Park on Thursday. The former NBA champion with the Dallas Mavericks in in Australia with his family. Zverev, who is back in action after a long-term ankle injury, will kick off the first Grand Slam of the year against Peru’s Juan Pablo Varillas. Nowitzki played tennis in his youth before basketball. “I started when I was five and liked the competition. I was ranked sixth or seventh in Bavaria,” he once told broadcasters Tennis Channel. Later, …