Kaita was dismissed for kicking a Greek defender on the touchline last Thursday as Nigeria lost 2-1 to Greece, their second defeat at the World Cup.
On Sunday, team spokesman Peterside Idah said the player had received "more than 1,000 threats to his email from within Nigeria" and the team were "taking these threats very seriously".
"There's nothing official that's really come out that there's been a threat on Kaita's life," Idah told a news conference on Monday.
"It's just rumours and his friends talking about it. There's nothing official that we can begin to panic.
"In our language, if we say 'we will kill you', it means we are not happy with you. If a German hears 'I will kill you', it means you are dying next week. We really need to clear up this matter."
Midfielder Dickson Etuhu said although the players sympathised with Kaitu, they would not allow the threats, real or rumoured, to impact on their decisive Group B match against South Korea on Tuesday.
"At the end of the day of, we are all professionals and we have been playing under pressure for a long time," he said. "We have to deal with it.
"Football is a passionate game and people sometimes say silly things."
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