Norwich will be without Gary Doherty for three months after the defender underwent an exploratory ankle operation.
The centre-back sustained the injury in last week's friendly with Ahlafors IF to leave the Canaries short of defensive cover ahead of the new season.
Norwich begin their Championship campaign on 9th August at Coventry and boss Glenn Roeder admits he is trying to sign a new defender as a replacement for Doherty.
"It is bad news," said Roeder. "The scan revealed more serious damage than we thought and he had an operation to clean up the mess that is in his ankle.
"He will not play football for three months.
"That brings us down to three centre-backs and I want four. I'm working on bringing one in before the (transfer) window closes."
Meanwhile, Roeder has confirmed he expects to sign a striker within the next two days.
Roeder revealed he has been following an unnamed youngster throughout pre-season after being tipped off by another manager.
Asked if his main focus was still signing a forward, Roeder added: "There will be one in the next 48 hours that is of six foot in stature but you wouldn't think of him as a big striker, he is just a beautiful mover.
"The manager who has helped us out with this transfer has hopefully done Norwich a big favour because we have watched him twice in pre-season and he has been absolutely fantastic. He looks a serious young player.
"He won't be a big name to us at the moment but hopefully he will have a good season here at Norwich."