Neymar has likely been ruled out of Barcelona's season-opening game against Elche after spraining his ankle.
The Brazilian forward has only just recovered from the cracked vertebra he suffered at the World Cup finals and was back in full training ahead of Sunday's Primera Division match at the Nou Camp.
But a statement published on Barca's official website read: ''Following the Thursday training session Neymar complained about some pain in his left ankle, and tests have confirmed that the player has a Grade 1 ankle sprain.
''The club's medical team has indicated that his return to training will depend on how the injury treatment evolves.''
The fresh setback comes only days after the 22-year-old scored twice in a 6-0 friendly victory over Leon.
The statement continued: ''It's worth recalling that, last Monday, Neymar received his medical discharge from the back injury that he suffered during the World Cup in Brazil, and was able to take part in the Joan Gamper Trophy match on the same day.''
Barca were unable to offer a prognosis on Friday morning but it is likely Neymar will struggle to recuperate in time to face Villarreal at El Madrigal on August 31.
Despite that setback, veteran playmaker Xavi insisted the mood in the camp was good and said it was vital for the club to win ``at least one important title'' under new coach Luis Enrique following Gerardo Martino's exit.
``That is a nice challenge,'' he told reporters at a press conference.
``Barcelona cannot afford another season without results. Last year was not good and we have to forget it. We have got a clean slate to move forward.''
Xavi also agreed with team-mate Dani Alves that the players should take the blame for last season's disappointments, not Martino and his staff.
Barca forward Pedro is hoping to recover in time from a bout of gastroenteritis, while German goalkeeper Marc-Andre ter Stegen (back) and Belgian defender Thomas Vermaelen (hamstring) are set to miss out against Elche.
The visitors have been boosted by the news that defender Jose Angel has agreed a contract extension until 2017.
Fellow defender David Lomban told the club's official website: ``We will need to produce a perfect performance to take anything positive away from the Nou Camp.''