World No.2 Rafael Nadal pulled out of the Mexican Open, cutting short his comeback from a hip injury when the problem flared up again.
The 31-year-old Spaniard was visibly downcast as he discussed the continued problems.
"My goal and hope was to play in this tournament," he said at a press conference on Tuesday in Acapulco.
"Unfortunately, in my last training session yesterday, I felt a sharp pain in my leg again."
Nadal, favoured to win the tournament, had been due to face fellow Spaniard Feliciano Lopez.
He is unsure if he will play at the Indian Wells and Miami Masters tournaments in March.
"I took all the appropriate steps to arrive at the tournament in form. I went to Cozumel first, to adapt (to the climate)," he told reporters.
"But yesterday, in my last training session before the tournament, during one movement I felt a sharp pain again in the same area where I had the problem in Australia."
Nadal limped out of the quarter-finals at the Australian Open on January 23, and he has since lost his No.1 ranking to Roger Federer.
The 2017 Roland Garros and US Open champion said doctors in Mexico warned him not to play for fear of aggravating the injury.
"I still don't know what it is, because we don't know. It seems it's not as bad as what I had at the Australian Open," he said.
"Now, my main goal is to find out the extent of the injury."
This marks the fifth tournament in a row that Nadal has pulled out of or retired from -- the Australian Open, Brisbane, London, Paris and Acapulco.
Earlier in the week, the 16-time Grand Slam winner Nadal announced himself fully fit and said he was looking forward to competing again.
"I took a couple of weeks of rest and worked hard on rehabilitation," he told reporters prior to pulling out.
"Last week, I started practising hard again. I feel ready."
Nadal is expected to remain at least one more day in Acapulco to have more tests done.
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"Maybe it is a minor situation, but the reality is that there is liquid and until it goes down a bit and the relevant tests are done, it will not be possible to diagnose," he said.
While a victory this week would not have been good enough to overhaul Federer, it would leave Nadal primed to replace the Swiss star at Indian Wells or Miami next month.
The 2008 Olympic gold medal winner is known as the "King of Clay" and is considered the greatest clay-court player in the history of the sport.
But his success is not limited to clay. Nadal has won 10 French Open titles, three US Opens, two Wimbledons and one Australian Open.