Defour picked up a hamstring injury in Burnley's 3-1 defeat against Southampton at the weekend and Dyche is still waiting to discover the full extent of the damage.
This weekend's clash against Everton will surely come too soon for the Belgium international midfielder, but Dyche is unable to say until the scan results return.
“I don’t know yet, it’s too early to say," he said. “I think it’s a hamstring, so it’s too early to tell the severity.”
Dyche was also unwilling to say whether Defour's 90-minute run-out for Belgium against Gilbraltar on Monday night was a contributing factor.
“You can never guarantee that (fatigue after international duty), it’s hard to define, we look at the stats and up against their training load, and it’s hard," he added.
“I’ve no clue (for Everton). That’s not ideal but, on the other hand, it gave young Aiden (O’Neill) another chance. He’s 18 and doing a really good job, and maturing nicely. It will do him no harm at all, even in tough circumstances like that. It’s part of your growth as a player.”