MILLWALL'S Shaun Williams is a doubt for this weekend's pivotal Sky Bet League One clash away at second-placed Walsall.
Neil Harris confirmed the midfielder failed a late fitness test before Tuesday night's Johnstone's Paint Trophy second leg win at Oxford after injuring his foot against Crewe last weekend.
Williams fractured his foot against Wigan last April and missed part of pre-season training, and it seems the midfielder aggravated the injury challenging for a ball against the Railwaymen.
"He was a disappointed young man as you'd expect," Harris said. "He's such an important player for us and I think we missed him.
"We'll be a lot clearer on him on Thursday morning, it's too early to tell now."
If Williams recovers before the weekend he could be an option at centre-back with Mark Beevers suspended for the fixture at the Bescott Stadium.
Harris revealed after Tuesday's ultimately fruitless attempts to recover from a 2-0 defeat in the first leg against Oxford that Millwall prepare for the possibility of being down to 10 men.
The Lions played the last 25 minutes a man down with Harris bringin on Fred Onyedinma as they sought another goal to level the tie on aggregate.
But the Millwall boss admitted that it's a different prospect in the heat of battle.
Harris said: "We always think about 10 players but it's difficult to think about it during a semi-final second leg when you're chasing the game. Where do you go?
"Sometimes when you've got seven subs it's easier but with five the options are less.
"We had to try to balance it out by trying to get on the front foot to score a goal.
"We had to put an out-and-out wide player at right-back and had a very attack-minded left-back with three centre-forwards on the pitch and then Fred on to run at the opposition. We've had a right go.
"I'd no complaints about the sending off. Mark will be disappointed because he'll miss out on Saturday.
"There's an opportunity for Sid Nelson. Joe Martin came on and did really well, he's played left-sided centre-half before. And Shaun Williams can play there as well."