On Monday, Nadal – who has 4.5 million followers on Twitter – wrote "Today we have lost one of the most important and relevant people in our world. Rest in peace #NelsonMandela".
Here is the original tweet, in Spanish:
Which was all very well – except the 94-year-old former President of South Africa was not dead.
Rather predictably, the storm surrounding Nadal’s comment – which was re-tweeted more than 3,000 times – resulted in an embarrassing retraction.
"I had incorrect information and for now #NelsonMandela has not left us," Nadal wrote soon afterwards.
"I hope that he is with us for a long time; what he did will be with us forever."
Mandela, or 'Madiba' as he is affectionately known, is gravely ill in hospital after being checked in with a lung infection.
The former freedom fighter, who was jailed for 27 years by the racist Apartheid-era South African government, has suffered from poor health in recent years.
This is the fourth time he has been hospitalised for lung or respiratory problems in the past two years, and with his condition described as 'serious' many are concerned this may be one battle too many for the veteran statesman.