The midfielder was struck by a water bottle thrown from an Arsenal section of the stands during the Carabao Cup quarterfinal which Tottenham won 2-0 to reach its first semifinal since 2015.
“I saw it and it was lucky that it wasn’t a big issue,” Pochettino told reporters.
“We play a derby and we hate each other in a good way but it is in a bad way when you go to damage some people or an opponent.
“It is only one stupid person who made a mistake. I respect the Arsenal fans. For one, you cannot talk about everyone.
“I hope that Arsenal take responsibility and, through the cameras, they can identify [who it was]. It wasn’t a problem but it could have been a big problem, some big issue and how are we going to fix it?”
Ali had been walking away from the touchline when he was hit in the 73rd minute. He responded by making a 2-0 gesture with his hands towards the home supporters.
The 22-year-old, who had set up Son Heung-min’s opening goal and scored the second, said victory was made a “little bit sweeter.”