Mendy turned and swung his right arm in Lamela's direction in the 92nd minute at Wembley, though did not make contact with the Tottenham winger.
The off-the-ball incident went unpunished by referee Kevin Friend but, having occurred directly in front of an assistant referee, it was spotted by the team of match officials at the time.
Mendy will not, therefore, face retrospective action from the Football Association.
Lamela came close to equalising and potentially salvaging a point for Tottenham shortly before the incident, only to hit Dele Alli's pass over the crossbar.
Delays to the construction of Tottenham's new stadium led the match to be played at the national stadium, just a day after an NFL match between Jacksonville Jaguars and Philadelphia Eagles was held there.
"When the ball was going to Erik I said ‘goal’ but no, watching the replay, the ball just bounced before his boot and that is why he missed," said Pochettino.
Guardiola added: “Lamela had a clear chance and due to the grass they did not score. If the grass is good, Lamela with his quality in his left foot is in a better position to score a goal.”
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