Japan's former world No. 4 Kei Nishikori pulled out of the men's singles qualifying first round at the Australian Open on Tuesday.The 36-year-old, currently ranked 237th, signaled discomfort in his shoulder during his 30-minute warm-up in Melbourne ahead of his match against 250th-ranked Kimmer Coppejans of Belgium.A week ago, the same issue saw Nishikori retire in the first round of the Canberra International, an ATP Challenger 125 event.Nishikori lost in the second round of the Australian Open last year before sitting out the French Open, Wimbledon and the U.S. Open, all with lower back p…READ FULL ARTICLE