Nick Powell Wigan Athletic return KO 'unnecessary' - Stoke boss
Former Latics favourite Powell was given a second yellow card with barely a minute remaining of the 2-0 defeat to fellow relegation candidates Boro.
The subsequent one-match suspension prevents him returning to the DW Stadium, where he called the tune during his three-year stay which ended last summer.
And O'Neill, himself a former Wigan man, admits his loss will be a huge blow.
“Nick's sending off is unnecessary," mused the Stoke chief. "It doesn’t help us at all in any shape or form.
"And some of our decision-making when we went behind in the game was extremely poor.
“It was in terms of possession, and even just little things like our delivery at set pieces. All of those things.
"You can just hear the anxiety creeping into the players because they have gone behind in the game.
“That is something that we have to make sure we deal with in the remaining seven games.”