MELBOURNE (Reuters) - Tennis authorities have encountered “challenges” over the arrival dates of players in Australia ahead of the new 2021 season, the men’s ATP Tour said on Tuesday, throwing the ATP Cup and other Australian Open leadup events into doubt.Tennis Australia (TA) had planned for players to arrive in the southern state of Victoria by mid-December to give them time to undertake a mandatory two-week quarantine before competing but the ATP said that was now under review. “In discussions with Tennis Australia over the past 24 hours, we have been informed there are some new challenges around the previously planned arrival dates for players and team members,” the ATP said in note to players. “We continue to work with Tennis Australia on confirming plans for January, and we will provide an update as soon as more information is available in the coming days. “We understand there is uncertainty about the start of the 2021 season, and we are working as hard as possible to deliver the best possible calendar of events to players.”