Rafael Nadal has tested positive for Covid-19 after returning home from the Mubadala World Tennis Championship in Abu Dhabi.
The 20-time Grand Slam champion was beaten by Britain's Andy Murray in the semi-finals of the exhibition event on Friday.
Nadal said he had experienced some "unpleasant moments" but hopes to improve "little by little".
The 35-year-old has only just returned to action after a long injury lay-off.
 Nadal wrote on Twitter: "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.
"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 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."
Nadal made his comeback in Abu Dhabi after a foot injury had ruled him out of the final months of the 2021 season.
The Spaniard had planned to play in an ATP tournament in Melbourne before competing at the Australian Open, which starts on 17 January.
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