The manager was nearly floored by a spectator that was coming from the away end, but a player intervened.
The incident occurred during the Carabao Cup third round clash with Walsall.
While the invader did get onto the pitch, he was blocked off by Walsall's Dave Okagbue.
Cooper insisted afterwards: "I didn’t really see it. But I obviously heard the chanting in the crowd and I’ll own that.
"You’ll never hear me showing any disrespect towards the fans’ opinion of you. That’s what a supporter is, he needs to support his club in how he sees fit.
"I’ve obviously got to build some credit here with the supporters and earn the right to do the job. But I knew that anyway.
"Things like that will make me even more determined to do well because I’m desperate to do that. I’ve absolutely no problem with it."