Madrid, 20 December 2021 (dpa/MIA) - Rafael Nadal has tested positive for coronavirus on his return to Spain, leaving his participation at the Australian Open in doubt. The 20-time major champion played at the Mubadala Tennis Championship in Abu Dhabi last weekend and declared his mission a success despite consecutive defeats on his return from a foot injury. Indeed, Nadal had only competed in two matches since losing to Novak Djokovic in the French Open semi-finals in June before testing his long-term foot problem against Andy Murray and most recently Denis Shapovalov. However, the 35-year-old's plans to feature in the Melbourne ATP 250 ahead of the Australian Open in early January have suffered a setback after he tested positive for Covid-19 upon landing in his home country on Monday. Nadal revealed the news on Twitter as he posted: "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. "Both in Kuwait and Abu Dhabi we passed controls every two days and all were negative, the last being on Friday and having the results on Saturday. "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 analyse my options. I will keep you informed of any decisions about my future tournaments!" Nadal was eyeing the Australian Open, which starts on January 17, as his first major comeback, though he earlier admitted his entry was not guaranteed as he evaluated his foot injury and physical fitness. "I cannot guarantee Australia 100 per cent, because I need to go home and see how the body responds after these days," Nadal told reporters on Saturday. "I have time to make a decision. At this point in my career, I need to go day by day, study each movement well. "I have been able to show a competitive level against good players even without being in perfect condition. There are things to improve but looking at things with perspective it has been a positive tournament [in Abu Dhabi]. "The main objective is to be healthy enough to do the things that I need to do and aspire to the objectives that I have always had." The ATP Tour event in Melbourne, which would be Nadal's first such tournament since August, is due to start on January 3.