Sunderland defender Luke O'Nien was involved in an incident with a Portsmouth supporter during yesterday's League One play-off semi-final second leg at Fratton Park.
The incident occurred when O'Nien took a tumble over the advertising hoardings whilst chasing the ball and led to an angry fan being escorted from the stand.
After the game, Sunderland's popular 24-year-old midfielder played down the incident as "just a bit of handbags".
Sunderland sealed a 1-0 aggregate win to reach the final at Wembley against either Doncaster Rovers or Charlton Athletic.
"It's nothing to think about too much," added O'Nien. "It's happened and it's very silly.
"I've seen my little cousin hit harder than that, so not a problem with that."
O'Nien then said he was asked by police if he wanted to press charges after the game, but declined.
Sunderland manager Jack Ross said the incident during the goalless draw "wasn't great" but that he "wouldn't make a big deal of it".
However, Cattermole told BBC Radio 5 Live: "He was punched in the back - I was very disappointed and very surprised that people think they can do that when they come to watch a game.
"Someone like Luke as well, he's a fantastic lad. He doesn't need or deserve that.
"It was a tense atmosphere, I've played here a few times. It's a great ground with a cracking support and it's a shame sometimes one lets them down.