The 35-year-old Spaniard posted a photo of himself on an Australian Open court, along with the caption: "Don't tell anyone ... here I am".
Winner of 20 Grand Slam tournaments, Nadal tested positive for Covid-19 upon his return to Spain following the Abu Dhabi exhibition tournament, like other players including Denis Shapovalov, Andrey Rublev, Belinda Bencic and Ons Jabeur.
Britain's Emma Raducanu, winner of the US Open this year, had tested positive before the tournament.
His arrival will be a boost for the organizers of the first grand slam of the year, which will take place from January 17 to 30 in the absence of many stars from the world circuit.
Serena Williams, Roger Federer, Dominic Thiem, Jennifer Brady, Karolina Pliskova and Bianca Andreescu will miss due to injuries.
The presence of world No.1 Novak Djokovic, also winner of 20 grand slam tournaments, remains the main questioning of the tournament.
The 34-year-old Serbian withdrew from the ATP Cup before the start of the competition, raising doubts about his participation in the Australian Open, of which he is the title holder.
Djokovic, who holds the record for victories in this tournament (nine), has so far refused to confirm whether he was vaccinated against Covid-19, a condition required to participate in the tournament unless he has a medical exemption.
© 2021 AFP