The 20-time grand slam winner announced in August that his season was over, as he battles a problem that has troubled him since 2005 and has recently hindered his tournament preparation.
Nadal felt he was unable to do himself justice, and since a French Open semi-final defeat to Novak Djokovic in June, he has played just two more matches, reaching the Round of 16 at the Citi Open in Washington.
He wrote on Instagram: "Hello everyone, I have not communicated with you through the networks for some time.
"I can tell you that I was in Barcelona with my team and the medical team, to receive a treatment on my foot that will mean I take a few days of rest and a few weeks off court.
"I am back home and in the process of recovery. Thank you all for your support!"
The social media post shows Mallorca native Nadal giving a thumbs-up gesture to the camera, but it also gives an indication of the extent of his problem.
He stands with only his right foot on the ground, the left raised off the floor in what looks like an effort to protect it, as he props himself up with a pair of crutches in his left hand.
Nadal has won the US Open four times, most recently in 2019, but has been one of a number of star-name absentees from this year's tournament in New York.
The 35-year-old has 13 French Open wins among his haul of majors, and stands level on 20 grand slams with Roger Federer and Novak Djokovic.
Djokovic has an opportunity to go top of the all-time men's list on Monday (AEST) when he faces Daniil Medvedev in the men's final at Flushing Meadows.
As Nadal suffers, so does his great rival Federer. A Nadal return to action in 2022 appears a more likely prospect than another Federer comeback.
Federer has cast some doubt on whether he will play again, as the 40-year-old battles knee trouble.
The Swiss said last month he would be "on crutches for many weeks" after surgery, declaring he wanted to give himself "a glimmer of hope" of featuring again on the ATP Tour.