NEIL Harris has warned his players they must be "on their toes" as he aims to add at least two players to his squad this month.
Harris was furious with how his side let Norwich back into the game last Monday as the Lions left Carrow Road without a point after a 2-1 defeat.
The Millwall boss has made no secret that the FA Cup is not the priority this season, and he could opt to give players such as Kris Twardek, David Martin and Ben Thompson starts against Barnsley at The Den on Saturday.
Tykes boss Paul Heckingbottom could also leave out several first-team regulars. Both sides are in the bottom half of the table after 26 games, and both could be fighting a relegation battle in the second half of the season.
Millwall can't afford to lose any more players to injury. James Meredith, Shaun Hutchinson and George Saville have played in every league game this season, and Harris could opt to give them a rest ahead of the next league game at home to Preston. Saville has played 31 times this season including internationals.
Alternatively, Harris may decide to give those who featured at Norwich the chance to redeem themselves.
Harris was asked if it would be difficult to lift his players after Monday's loss and he responded: "Lift my players? No, I left them in no uncertain terms what my thoughts were about the second-half performance.
He added: "We're in the January transfer window and people need to be on their toes. Every window while I've been in charge we've signed better players. That has to continue now. It's not an easy window to try and buy players in, it's a sellers' market in January.
"We'd like a couple of players into the building as quickly as possible to boost our group. We are a small group and we have limited options to make changes.
"The most important thing is to get the right players, that's key. But the sooner the better.
"The FA Cup run we had last year was outstanding, it really boosted us financially as a club and on the pitch as well, beating three Premier League sides.
"It's not the most glamourous tie, Barnsley at home, for me or Paul. We'd both much rather focus on the league. However, it's an opportunity for people to perform better than they did [Monday].
"We'll reflect on that game. You give people an opportunity and you expect them to stake a claim for the next game, some players didn't do that. Certainly the subs that came on were non-existent."
Millwall have lost five successive games against Barnsley, the last four with Harris in charge. The Lions reached the quarter-finals of last year's competition before losing to Tottenham. Barnsley were knocked out by Blackpool in the third round.
Millwall record against Barnsley
Won 21 Drew 12 Lost 24
Possible Millwall team
4-4-2: Archer; McLaughlin, Hutchinson, Cooper, Craig; Wallace, Tunnicliffe, Williams, O'Brien; Onyedinma, Morison.
Millwall 1/1 Draw 23/10 Barnsley 13/5
Image: Millwall FC