Sheffield United striker Billy Sharp was headbutted by a fan in the midst of a pitch invasion following the play-off semi-final defeat at Nottingham Forest.
A quite brilliant tie came to a dramatic conclusion as Forest keeper Brice Samba saved three penalties after a 3-3 aggregate draw.
After he saved the final one from Morgan Gibbs-White to send Forest to Wembley for the first time since 1992, home fans streamed onto the pitch to celebrate.
Sharp was stood by the side of the pitch and appeared to be blindsided by the fan, who went directly for him before running off.
"It's assault," Blades boss Paul Heckingbottom told Sky Sports after the game. "We've seen one of our players attacked.
"He's shook up, bleeding, angry. It'll be dealt with.
"We're seeing things thrown on the pitch and things that are thrown on putting players' health and safety in danger and nothing's ever done about it.
"There will be something done about that. We've seen what's happened, we know what's happened. There's a prison sentence there without a doubt.
"How can you come to a place of work minding your own business and be assaulted in that fashion?
"It's just bang out of order and it's everything that's wrong. Too many times we hear people condemn it, but nothing's done about it. We're the ones that suffered.
"It's upsetting for a lot of reasons - I don't want to say too much more about it. He'll be dealt with."
Reports form the City Ground claim Sharpe received treatment at the ground, with Sheffield United officials promising that legal action against the fan will be sought.