The Magpies' first-choice goalkeeper will not feature again this season after dislocating his shoulder in Sunday's 3-0 hammering at home in the Tyne-Wear derby.
Krul landed awkwardly after punching the ball clear during the match, and he was swiftly replaced by Rob Elliot on 57 minutes before being taken to hospital for assessment.
The Dutchman's injury comes as an additional bitter pill to swallow for Toon boss Alan Pardew, who believes his side failed to recover from Thursday's 1-1 Europa League draw with Benfica that saw the Magpies crash out 4-2 on a aggregate.
"I don't feel particularly great, it was a tough day really," Pardew told reporters. "They looked like a team that had worked all week on us, and we looked like a team that had a really tough game on Thursday night.
"We looked a little bit tired in our minds and our fitness and our application to the game. We were always struggling in that game. Unfortunately it turned out to be a great day for Sunderland and an awful day for us.
"To our fans, that's everything and we just have to make sure that in the last five games we put that right and get some work in on the training ground.
"Three or four of our players never trained after Thursday night, just a short warm-up and a massage. [Yohan] Cabaye looked really tired, Mapou [Yanga-Mbiwa] particualrly, even Papiss [Cisse] looked a little bit tired and it's enough at this level."
Pardew said the defeat was one of the lowest points of his tenure at St James' Park and has demanded a response from his players between now and the end of the season.
"It's up there for sure because the team just didn't perform today as we would have wanted and most of the things that we attempted to do in the game didn't come off," Pardew said.
"Losing Tim lost me a pair of legs on the field and it only really left me with only one sub which was difficult.
"It's about us making sure that we put perfomances in until the end of the season that can help to ease the memory of this defeat.
"It won't go away, we're going to have to wear it, probably next year as well. We're under no illusions of the responsibility we have to our fans and we let them down today 100 percent."