Hungary striker Sandor Torghelle has not fully recovered from his ankle injury, Neil Shipperley is just back from knee problems and Ivan Kaviedes is still not fully fit.
Leeds chief executive Shaun Harvey said: "We had agreed everything financially with Palace and were hoping to complete the deal, but they have been hit a by a few injuries and until they have assessed, the deals can't go through.
"There's still every opportunity that the deal will be concluded early next week."