Millwall winger Aiden O'Brien says the 3-1 defeat to Barnsley was a 'wake-up call' for the team.

The Lions were looking to improve on a four-match unbeaten streak after a late resurgence against Reading secured them all three points.

However, a brace from Tom Bradshaw and then a late penalty converted by substitute Mamadou Thiam meant that the visiting Tykes would leave south east London with their first victory in four.

O'Brien said: "Us as a team, we cannot afford to be 60 percent, 50 percent, or 80 percent even. We’ve got to be 100 percent every game if we want to go out and actually compete in this league, because it’s a hard league.

"We can’t afford to be slacking in any areas of the pitch, we’ve got to be on it every game. And when we are on it it’s frightening, which we have shown.

"We never really lose like that at home, it’s very rare we lose like that at home and we’ve just got to learn from that now. 

"It’s a learning curve, and we’ve just got to come back from the international break and show everyone that we’re much better than that.

"So yeah, definitely [it is] a wake up call."

Millwall were without midfielder Shaun Williams, as his absence is said to last around three months according to Neil Harris.

Former Manchester United academy player Ryan Tunnicliffe replaced him for his first full start this season, seeing out the full 90 minutes alongside George Saville.

While Tunnicliffe will relish the opportunity to receive consistent playing time, provided he can remain fit and perform well, the loss of Williams will hurt the Lions.

Asked whether Williams is one of the club's standout performers, he said: "Yeah, for me he is always one of our standout performers, that’s me on a personal level once again.

"I always feel that with Shaun Williams in the team, he gets the ball going, that ticking. He gets on the ball and he’s one of our star men because, without him in the team, we don’t usually get on the ball and kind of make things tick.

"He’s definitely going to be a huge miss.

"I feel that he can offer a lot Cliffy [Ryan Tunnicliffe], I reckon he can add a few goals to his game because he’s always in and around it [the box]. 

"But you know, it’s his first game, first kind of start in the league, so you’ve got to give him some sort of time to kind of gel in with the team. But I thought he did well today."