Dele Alli being struck by a plastic bottle thrown from the stands at Emirates Stadium showed the north London derby rivalry "in a bad way", according to Mauricio Pochettino.
Tottenham playmaker Alli was hit in the head by the missile in the 73rd minute of the EFL Cup quarter-final clash and responded with a '2-0' gesture to nearby Arsenal supporters.
The incident comes after projectiles thrown when Pierre-Emerick Aubameyang scored a penalty in Arsenal's 4-2 win over Spurs in the Premier League on December 2 included a banana skin.
Alli set up Son Heung-min for the opening goal and sealed a 2-0 victory for Spurs with an impudent chip beyond Petr Cech in the 59th minute.
Pochettino felt the incident involving Alli showed a negative aspect of the feelings between the rival clubs.
"Lucky that it wasn't a big issue. Come on, when we play a derby we hate each other in a good way, but that looks in a bad way, looking to damage an opponent," said Pochettino.
"I cannot talk in general [terms] because only one stupid person made a mistake."
Arsenal boss Unai Emery claimed not to witness the event but stated it is not acceptable.
Emery said: "I didn't see. I thought the atmosphere in the stadium was good. If there is a situation like that, then it is not good behaviour."
Tottenham will face Chelsea in the EFL Cup semi-finals, while holders Manchester City were drawn against League One outfit Burton Albion.
