The hosts swiftly condemned the individual targeting the away dugout, while Swansea's squad closed ranks behind their team-mate.
In an official statement, Millwall confirmed they were "aware of an alleged, individual incident of discriminatory abuse towards a Swansea City player during the second half" before adding: "The club operates a zero-tolerance policy towards any form of discriminatory abuse. Any individual found to have engaged in such behaviour will face the strongest possible action.
"The club is working alongside the relevant authorities to establish the facts and is unable to comment further as tonight's alleged incident is the subject of an ongoing police investigation, which the club fully supports."
Reassuring supporters that Eom is receiving full pastoral care, Matos added: "He is a smart kid, he is not happy with the situation but he knows we will stay with him and follow the situation as long as we can. Millwall did the right thing by announcing there is no place for this sort of thing. I'm happy with how it was handled, but really sad that it happened. Now it is about evaluating the situation and we'll see what happens."