Newcastle boss Alan Pardew said his squad is being tested "to its limit" as they look to recover from three defeats in four Premier League games.
Injuries to Steven Taylor and Fabricio Coloccini led to a reshuffled back four at Norwich and a 4-2 defeat.
"It's fairly obvious we missed them," Pardew conceded. "Our squad has been stretched to the limit.
"You can't concede from three set-plays but any team would struggle with the injuries we've got in central defence."
Newcastle's latest defeat means they have taken just one point from four league games and dropped out of the top six.
Pardew added: "We don't need any more blows, particularly injury-wise. We have to keep our spirit about us and we showed that today. We want to stay in the top seven or eight if we can.
"We created chances all day [against Norwich] and we looked like we were going to score. We accepted that we weren't going to keep a clean sheet and that we had to score goals."
But the Newcastle boss found some positives in his side's defensive display at Carrow Road.
"We did very well other than the set-plays," he added.
"[Steve] Morison and [Grant] Holt are a handful and so was [Wes] Hoolahan in behind. They gave us some tough times."
As well as having their central defensive pairing out injured, Newcastle are also without Martin Williamson, Danny Guthrie and Cheick Tiote. But Pardew expects "one or two" players to return in the near future.