The world No.2 is therefore unlikely to play again until the season's first Masters event in Miami from 25 March (AEDT).
"I am very sorry not to participate in Acapulco 2021," the 34-year-old Nadal, champion in Acapulco in 2005, 2013 and 2020 wrote on Twitter.
Lamento mucho no participar en Acapulco 2021. Es un año difícil para todos y en mi actual estado de salud, con dolencia en la espalda, hace imposible realizar un viaje tan largo. Me encanta Acapulco, jugado los últimos 4 años, pero este año no ha sido posible. Ojalá en 2022! 😉— Rafa Nadal (@RafaelNadal) February 26, 2021
"It is a difficult year for everyone and in my current state of health, with a bad back, it is impossible to make such a long trip.
"I love Acapulco, I have played the last four years, but this year it is not possible. Hopefully in 2022!"
Nadal, a 20-time grand slam title winner, was bothered by the back injury in Melbourne where he was knocked out of the Australian Open in the quarter-finals by Stefanos Tsitsipas from two sets up.
The Spanish star could lose his No.2 world ranking next week to Russia's Daniil Medvedev if the Australian Open runner-up makes the final in Rotterdam.