The Reds Head Coach was speaking after today's final pre-season friendly ended in a 4-0 defeat away at Rotherham United.
Paul Heckingbottom cut a frustrated figure following today's defeat at the New York Stadium, having seen his charges ship four second half goals to end pre-season in disappointing fashion.
The 4-0 defeat disappointed Heckingbottom, but the manner of the players' performances equally came in for criticism from the Head Coach.
With just a week to go until the Sky Bet Championship campaign kicks off with an opening day trip to Bristol City, Hecky told the awaiting press post-match that this afternoon should act as a wake-up call.
"We aren't a five-a-side team" he said. "The players have to realise that you can't play fancy, you can't be soft in the Championship. You have to run hard, you've got to head the ball and want to win tackles. The only player definitely in contention for a start next week is Joe Williams because at least he got stuck in and made tackles.
"Maybe the players will start listening to me now. Instead of thinking I'm just being negative. We got away with murder at Rochdale on Tuesday, and I told them that. But it's the same again today only we've been punished."
The Reds could have been ahead early on when Adam Hammill had the chance to score from the penalty spot, following a foul on Ike Ugbo, but the Reds winger saw his spot kick saved.
Heckingbottom felt the Reds didn't deserve anything from the game but hoped that by next week the players would 'man up'.
"I keep saying it, but it's down to the players. You can't just be pretty players who don't want to get hurt at this level. You need to be men, you need to do the ugly stuff when the opposition have the ball and impose yourself on the game."
Lloyd Isgrove went off after a challenge in the first half but the Gaffer believes he should be okay and in contention for next weekend's game at Ashton Gate.
He said: "It was just a kick really, and of course he was frustrated to come off because they all need minutes in pre-season. But we need him fit and available for the first game."
Hecky isn't writing his squad off, but he reiterated the need for the players to learn quickly as we prepare for the 2017/18 Sky Bet Championship campaign.
"Of course we can go to Bristol and put in a good performance, but the players need to learn and fast."