Millwall manager Neil Harris felt today's meeting with Barnsley was perhaps a case of one game too many for his newly-promoted Championship side.

The Tykes emerged as deserved 3-1 victors from their trip to The Den and took the lead five minutes before the break through Tom Bradshaw.

Lee Gregory won and scored a penalty in first half stoppage time to ensure the hosts went in on level terms at the interval.

However, Bradshaw struck again on the hour before substitute Mamadou Thiam wrapped things up from the spot late on after Shane Ferguson was punished for fouling Jared Bird in the box.

Harris said: "I was disappointed with the performance of course. I was certainly disappointed with the outcome result wise "Was it a game too far for some of my players? Looking back now I would say undoubtedly yes. I would say obviously it was.

"I take responsibility for that because I pick the team, but what I will say is my players have been in excellent form individually and collectively and deserved the opportunity to play.

"If you were to take anything out of today for me just immediately after the final whistle I would say if we are not at our best Millwall standards in every fixture in the league this season we can get beat at any time, home or away.

"Today we weren't at our best. We weren't at our best as a defensive unit. We were too stretched, we gave the ball away cheaply and we got hurt on the transition.

"Ultimately if you give good players at this level opportunities obviously they are going to take them.

"Barnsley deserved to win the game because they took their chances."

And the Lions chief was quick to point out although today was a day to forget, overall Millwall's start to life back in the Championship has been positive.

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Lee Gregory scores his penalty | Picture: Benjamin Peters Photography

Harris added: "I'm really disappointed with the performance and the result.

"But ultimately over the first 11 games of the season I am delighted with what I have seen from my group."

However, Harris was keen to stress his squad can't afford to take any opponents lightly, as today proved against the Tykes.

He said: "The boys have set their own standards. To get in the top half of the league on Tuesday night (v Reading), having played a tough run of fixtures as well, maybe everyone just got a little bit carried away connected to the football club.

"Everyone just thought 'Well actually we are not a bad side here, we can be alright in this league. We will just turn up against Barnsley and win the game'.

"Well me and my staff didn't think that. If my players or fans had any inclination towards that view then that has gone out of the window for the rest of the season because anybody can beat us at any stage during this season unless we are at our best. Then we will games of football."

The manager also confirmed Shaun Williams now faces a lengthy spell on the treatment table.

"Shaun has got damage to his lateral ligament in his knee so we are looking at a period of about three months out," said Harris.