Johann Berg Gudmundsson has been ruled out of the Clarets' trip to Hull City on Saturday.
Gudmundsson limped out of Burnley's FA Cup defeat to Lincoln City last weekend and Dyche confirmed the Iceland international will not recover in time for the trip to Humberside.
"Johann has unfortunately tweaked a medial knee ligament, which is not too drastic but he's not going to be ready for the weekend," said the Burnley boss.
Gudmundsson had made just two appearances in the Cup since recovering from a hamstring injury sustained in the third-round tie at Sunderland in early January, and joins Steven Defour and Jeff Hendrick on the sidelines.
The visit to 18th-placed Hull will be the last game of Hendrick's three-match ban for his sending off at Watford at the start of the month.
Defour has returned to training following a spell back in Belgium for treatment to a hamstring injury, but is not ready to return after three games out.
"His injury is clear but now it's strength and fitness, of course, on the back of a few weeks out. He's actively back on the grass now," added Dyche.
Together with the absence of Dean Marney, Burnley's midfield resources have been stretched.
But Dyche is looking forward to an upturn in fortunes as the Clarets embark on a run of four successive away league games ahead of the next international break.
"By next week, possibly with a couple of the injuries, we might start re-forming as a total squad again," he said.
Goalkeeper Nick Pope will also be absent for Saturday's game at the KCOM Stadium, when the Clarets will be looking for a first away win of the season, after suffering an ankle injury in training ahead of last Saturday's cup upset.
But on the positive front, defender Kevin Long came through a mid-week behind-closed-doors friendly as he continues his return from minor knee surgery.