The confrontation is said to have occured not recently and instead after City's FA Cup final defeat to Manchester United in May, says the Daily Mail.
It's suggested the fan, with a Scouse accent, said to Guardiola, "right mate, just 'cause you lost" after the City manager walked past him.
The words sparked a response from Guardiola, who was twice held back by his entourage as he said multiple times, "do you know what is lost?", before being ushered away.
Watch below:
City were back to winning ways against Nottingham Forest midweek, ending a winless streak of six defeats and one draw in the past seven games.
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