Guardiola's initial comments came after his side's 5-0 victory over Sporting Lisbon in the 2021/22 Champions League last-16.
Nunes was plying his trade with the Portuguese giants at the time when the former Barcelona boss made the remarks.
However, Guardiola has revised his previous claim, acknowledging that Nunes is not yet among the world's elite, but emphasised he still considers him an exceptional player.
"Maybe I over-exaggerated a little bit. He's not [one of the best players in the world]. He is a really good player but sometimes, maybe I said this comment after a 5-0 win, it was actually 5-0? But he's an exceptional player," he told reporters.
Nunes joined Man City from Wolves on deadline day in the summer in a £52million deal.
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The 25-year-old has been involved in three games for the Sky Blues, and was given a start in the 2-0 win over Nottingham Forest last weekend.
He assisted Erling Haaland to double City's lead on the afternoon, with Phil Foden having already put Guardiola's troops one goal to the good.
Nunes is expected to play a key role in the coming matches, especially after Rodri's red card in Saturday's victory.
Man City are expected to ring around the changes when take on Newcastle United in the Carabao Cup on Wednesday night.
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The Sky Blues then return to Premier League action against Nunes' former club Wolves on Saturday as they look to maintain their perfect start to the season.