STEVE Lomas fears Scott Malone suffered a serious knee injury against Burnley.
The left back had to be substituted seven minutes into Saturday's 2-2 draw after landing awkwardly and later returned to the bench on crutches and wearing a protective boot.
"We're a little bit worried about Scott to be honest," Lomas said. "It's a knee injury but we won't know the extent of it until Monday.
"He's on crutches and we're genuinely concerned that it might be a bad one."
Goals from Scott McDonald and Danny Shittu had given the Lions an early lead at The Den, but the league leaders replied through Sam Vokes' header and Shane Lowry's own goal.
"When you go 2-0 up it's a delicate scoreline," Lomas said. "We wanted to get to half time at 2-0 but their goal was a little bit of misfortune – the cross cannons of Shane's shoulder and pops up for Vokes to score from three yards. I can't blame anyone for that.
"The second goal was poor. We needed to defend better, we didn't and paid the price for it. The lads xanax were all disappointed but the level of performances in the last three games have been very good but for small margins, a little bit of luck and a few decisions going our way, but we're not far away.
"I pay credit to the lads because Burnley are a good team and their front two are a handful. We hung in there. At 2-1 up maybe we need to take one of the half-chances we had and kill the game off, but it was another entertaining game for the fans. Performances have been a lot better and we are fighting and scrapping for each other."
Asked whether Millwall's league position does not accurately reflect their recent displays, Lomas added: "We are where we are. All managers will say the same – do I think we should have more points? Yeah, it is beyond doubt that we should be further up the league.
"We've played three of the top teams recently and competed with every one of them, so now we need to two or three wins to shoot us up the table because it's so tight."