Neymar lasted less than 25 minutes of his return to Barcelona's starting lineup for their King's Cup last 16 clash at Getafe as he was carried off on a stretcher with an ankle injury.
It is the latest setback for the Brazil forward who had not started a match for the Catalan side since Christmas due to a lack of match fitness and then a stomach bug last week.
Neymar twisted his ankle when he turned awkwardly close to the touchline and had to be replaced.
He has a tear to a "tendon of his right ankle", said a club statement, and further tests will be carried out on Friday.
However, Barca coach Gerardo Martino played down the extent of the injury after the match, which his side won 2-0 to progress to the quarter-finals 6-0 on aggregate.
"The situation didn't look good when you saw it happen and you thought he might be out for a while but thank God it is not as serious as it appeared and he'll be back playing soon," he told a news conference.
"The doctors after the game have said it is not so bad and so if tests confirm it then it is not something serious."
(Writing by Tim Hanlon in Barcelona; Editing by Ken Ferris)