Neymar promised to "come back stronger" after Paris Saint-Germain said on Monday the forward requires ankle surgery and will be out of action for three to four months.
The Brazilian, who injured his ankle on February 19 against Lille in Ligue 1, "has had several episodes of instability in his right ankle in recent years," said the club, adding that its medical staff "recommended a ligament repair operation to avoid a major risk of recurrence."
Neymar tweeted he would not be discouraged by his latest injury.
"I'll come back stronger," he wrote with a praying hands emoji.
Qatar-owned PSG said Neymar would go under the knife in Doha "in the next few days" and said it would take "three to four months before he can return to training with the team."
That would appear to end any prospect of Neymar playing again this season, with the Ligue 1 season due to end on June 3 and the Champions League final, if PSG were to get there, a week later in Istanbul.
PSG, still waiting for a maiden Champions League title, will bid to overturn a 1-0 first-leg deficit in the last 16 against Bayern Munich in Germany on Wednesday.
Neymar, who has scored 18 goals in all competitions for his club this season, was in fine form for the French champions before the World Cup break.
But the 31-year-old has netted only three times in nine appearances since returning from Qatar, where he injured the same ankle playing for Brazil.
He came off with a sprain in his country's 2-0 win over Serbia in their opening game and didn't play again in the group stage.
The ex-Barcelona man returned in the knockout rounds but Brazil lost to Croatia on penalties in the quarter-finals, despite Neymar putting them ahead in extra time in that game.
He has had injury problems at World Cups before.
In 2014, he suffered a broken vertebra in the quarterfinals against Colombia and missed the semi-final, which Brazil lost 7-1.
Neymar's fitness has been a regular concern for PSG, since he signed from Barcelona for a world-record fee of 222 million euros (US$264m) in 2017.
He has scored 118 goals in 173 games for PSG, but has missed more than 100 games due either to injury or suspension. In Ligue 1, he has played only 49 per cent of PSG's Ligue 1 matches since his arrival (112 out of 228).
In his first season at PSG, a fractured metatarsal ruled him out of the second leg of their Champions League last-16 tie against Real Madrid, which they lost.
He didn't play again for his club that season and faced a race against time to be fit to play for Brazil at that year's World Cup in Russia.
The following year another metatarsal injury saw him miss the last-16 tie against Manchester United as PSG again went out in the first knockout round.
PSG are also without Presnel Kimpembe against Bayern on Wednesday, with the France centre-back set to miss the rest of the season due to an achilles injury.
On Saturday, during the celebrations of Kylian Mbappe's club record 201st goal, Neymar ventured onto the pitch on crutches.
In his absence, Mbappe and Lionel Messi have eight goals and four assists between them in three games.