Ever-present Michael Keane will miss out for Burnley at home to Nottingham Forest tomorrow night.
Centre back Keane had played every minute of the Clarets' Championship campaign this season before being forced off after 33 minutes against Rotherham United on Saturday, feeling dazed after a head injury following an earlier collision with Millers keeper Lee Camp.
Keane was not knocked out in the incident, but protocol means he won't be considered for six days after the game, as boss Sean Dyche explained: "He won't be right, but that's mainly due to the guidelines we work under. He's feeling well in himself and we've had him thoroughly checked out, and he's all clear, just a bit of grogginess, but you have a six-day window at least, so we'll observe that properly with the medical team and take it from there.
"Six days is the FA guideline, then depending on symptoms.
"We'll just see how he is, today he feels better, slightly off but generally well, we've had all the necessary checks done, and he's being monitored.
"There's a lot more knowledge now and it's appropriate, there is better medical support."
James Tarkowski is expected to come in for his first start following his £3m move from Brentford, having replaced Keane at the weekend.
Dyche was pleased with him, coming into the game just before half-time: "As a defender, it's a tough one to come into a game like that, it was a tight one, and, as a centre half, you want to start the game really, but I thought he handled it very well and, of course, came off with a nice clean sheet."
Tarkowski came in on deadline day, and the timing could scarcely be better: "We felt it was an appropriate time to sign a centre back, and Duffo unfortunately has an injury, there's nothing too serious, but he's not been with us for a week.
"Kevin Long is back with us and he's done very well with Barnsley so we're pleased with that."
Lloyd Dyer is still building up his fitness after arriving as a free agent last Monday, and also won't be considered tomorrow night: "We're making sure he's right, people know the way we work, the intensity we work at, and you have to be able to deliver that.
"He'd had a sort of indifferent period of training in spells while sorting his business out with Watford, so he's got to make sure he's doing the work.
"He's a fit type anyway, but it's trying to get the real edge to your fitness where you can deliver for the first team.
"When we feel he's ready for that, he'll become part of the group."