Top scorer Demba Ba, new strike signing Papiss Demba Cisse and midfielder Cheick Tiote have not returned from the African Nations Cup, while defender Fabricio Coloccini also missed the 1-0 defeat at the Amex with a groin injury.
Toon boss Pardew said: "We've lost the core of this team and Coloccini as well.
"We knew they'd all be coming back for the next round so to lose in this game makes it all the more galling.
"I've no idea if they will be back for Wednesday's game against Blackburn. But I hope so. We've got a big week."