(CNN) -- Rafael Nadal has pulled out of next week's ATP tournament in Buenos Aires, posting an online video in which he apologized to both fans and organizers as he did so.
The world No. 1 said he has yet to train following the back injury that hindered his performance in last month's Australian Open final, which he lost to Switzerland's Stanislas Wawrinka.
The Copa Claro tournament starts on 10 February.
"I want to make an announcement that really fills me with sadness -- I will not be able to play in the tournament in Buenos Aires," he said in a video posted on his official YouTube page.
The news comes just two days after his team said that he was recovering well from the back problem, following a series of tests in Barcelona.
The 27-year-old, who passed up the chance to draw level with American Pete Sampras on 14 grand slam titles when losing in Melbourne, had hoped to train for the first time on Thursday.
His failure to do so prompted his online apology.
"Since I came back from the Australian Open with my back injury I have not been able to train," he said in Thursday's video, which came against a backdrop of several trophies.
"I had hoped to train this morning but could not because of a stomach virus.
"We are four days away from the tournament and without training and given what happened in Australia, it is impossible for me to prepare adequately for a competition as important as the one in Buenos Aires."
"I'm sorry to all my supporters and organizers, and am sad personally to be unable to return to Argentina, but I hope to come back stronger soon."
There was no word from the Spaniard on whether he believes he will be able to play in the future tournaments in Rio de Janeiro, Indian Wells and Miami.
Nadal played through the pain barrier in the final in Melbourne, saying afterwards that he would never want to quit a grand slam final.
Despite rallying to win the third set, the Spaniard was beaten 6-3 6-2 3-6 6-3.