NEIL Harris has revealed that Shaun Hutchinson is out for the "foreseeable future" with a knee injury.
The defender missed the Lions' 1-0 defeat at Rotherham on Sunday. Murray Wallace partnered Jake Cooper in the centre of defence.
Millwall lost for the second time this season after Sean Raggett headed home in the 20th minute.
"I'm frustrated, I've got to be honest, Rotherham did nowhere near enough to win the game today," Harris said. "That's twice in four days that we've thrown points away.
"Ultimately when you play Rotherham you've got to stand strong from dead-ball deliveries and be organised. For the majority of it we did but that one moment we get it wrong, we don't compete, make bad errors of judgement and the ball ends up in the back of the net.
"It's extremely disappointing to have two games in four days up in Yorkshire and come away with no points.
"At Hillsborough I was very disappointed with my group with the way we approached the game, the mentality and the way we played for 70 minutes. The last 20 minutes we dominated. But we gave two really poor goals away.
"Today we dominated the majority of the ball, used it wisely at times, but sometimes we could have done better. That's where we are at the moment as a group with the players we've got.
"The second half there was a lot of good play. I'd like to have seen us get a few more clear-cut chances but I never felt in any danger from Rotherham [in the second half], the goalkeeper [Jordan Archer] has made one save from a counter-attack.
"What we've learned from the last four days and last season is that you cannot give teams at this level a leg-up. You give them a chance to score, you give them cheap goals and you're chasing the game. It's very difficult.
"Rotherham got their noses in front and had something to cling to. It was very difficult for us to break them down. Fair play to them for standing strong after all we chucked at them. That's twice in four days my fans have had to travel a long way to see us give cheap goals away, three in two games.
"We've not affected the ball going the other way with enough quality."
Harris confirmed Byron Webster, who was on the bench at the New York Stadium, would start in the EFL Cup against Plymouth on Wednesday.
"Hutch has got a knee problem and is going to be out for the foreseeable future," Harris said. "Byron is still finding his way. He's a natural right-sided player. Webbie has been out a long time and has come so far. Even to have him back now fully fit is a bonus.
"He is still looking for the last couple of per cent. It would probably have been an unnecessary risk but he will certainly play Wednesday evening."
Harris added it was "unlikely" the Lions would go into the market this week for defensive reinforcements.
Image: Millwall FC