Brazil's star winced in pain when he walked off the field on Tuesday.
Neymar was forced to leave Brazil's training session in Sochi early on Tuesday with a sore ankle, according to team officials.
Brazil is coming off a 1–1 draw with Switzerland in its opening match of the 2018 World Cup. Brazil will play Costa Rica on Friday at Saint Petersburg Stadium.
Neymar told Brazilian media that there was nothing to worry about, and he is expected to return to training on Wednesday. Video at training captured the incident, which appeared to come in a routine exercise with his teammates.
Neymar recently returned from a fractured metatarsal suffered while playing for Paris Saint-Germain in a Champions League match in February. He missed the remainder of the season and just returned to action in a friendly vs. Croatia in which he scored a goal.