Aiden O'Brien has vowed that Millwall will "come back stronger" after the international break following last Saturday's 3-1 Sky Bet Championship defeat to Barnsley at The Den.
The Lions have enjoyed a relatively successful start to life back in the second tier, but suffered a second home defeat of the campaign at the hands of The Tykes last weekend.
O'Brien, who is currently away with the Republic of Ireland senior international squad for the very first time, was critical of Saturday's performance - a result that ensured a record of two wins, two draws and two defeats in September.
"We weren't ourselves," he said. "We didn't impose ourselves on the game like we usually do. We were reactive instead of proactive and we weren't first to every ball.
"We didn't play our game, I feel, and it cost us. We rarely lose like that at The Den and we have to learn from that and come back stronger after the international break."
The attacker went on to say that Millwall will need to approach every single Championship game with the same mindset if they are to compete and that the Barnsley loss was a "wake-up call".
"We were ready for the game. Everything we did in training was spot on and we were sharp heading into it. But it just didn't happen for us.
"As a team, we cannot afford to be at 50, 60 or 80% in matches. We have to be at 100% every game if we want to go out and compete in The Championship. It's a very hard League. We cannot be slacking in any area of the pitch.
"When we are on it, we're frightening - we've shown that. Saturday was a wake-up call."