Former World Number one Rafael Nadal, who returned to action at the Mubadala World Tennis Championship in Abu Dhabi last week, on Monday said that he has tested positive for COVID-19 upon arrival in Spain.The 20-time grand slam champion informed that his RT-PCR test has returned positive and he is experiencing 'unpleasant moments'."Hi all. I wanted to announce that on my return home after playing the Abu Dhabi tournament, I have tested positive for COVID in the PCR test that was performed on me when I arrived in Spain," Nadal said in a statement."I am having some unpleasant moments but I hope that I will improve little by little. I am now homebound and have reported the result to those who have been in contact with me. As a consequence of the situation, I have to have total flexibility with my calendar and I will analyze my options depending on my evolution. I will keep you informed of any decisions about my future tournaments. Thank you all in advance for your support and understanding," he added.He further said that he took COVID tests every two days while in Kuwait for the opening of his new Rafa Nadal Academy and in Abu Dhabi for the three-day exhibition event, with all his tests returning negative.Nadal, 35, spent four months on the sidelines with a foot injury. He was, earlier, forced to pull out of Wimbledon, the Tokyo Olympics and the US Open.There was uncertainty over the Spaniard's participation in the upcoming Australian Open, and now the contraction of virus further casts doubts on his Melbourne tour.