The 33-year-old scored in the 86th minute of Saturday's clash to give the Lions a 1-0 win over the Bantams and seal promotion to the Championship.
However, the full-time whistle prompted several dozen Millwall fans to storm the pitch, with club manager Neil Harris telling them to get back in the stands.
Speaking to Sky Sports News, Morison said after the game: "I can't talk, they are annoying me. The fans have ruined it for me at the moment. I can't celebrate."
However, he also hailed his side's promotion, adding: "It's fantastic to be back in the Championship. We'll have a good crack."
The result sees the East Londoners back in the second tier of English football after a two-year absence.