Steve McClaren fears Newcastle may have lost up to 20 Premier League points as a result of keeper Tim Krul's knee injury.
The Holland international will sit out the remainder of the campaign after damaging an anterior cruciate ligament in his country's Euro 2016 qualifier in Kazakhstan on Saturday with Rob Elliot ready to stand in for him.
McClaren said: "It's a massive blow for us, you're talking about one of the best players in our team. He's a vital player, very important, and he'd get us 18 or 20 points a season with the way he plays.
"To lose that is devastating. We've had a couple of days to get over it, but for him, the shock of starting to get injured is starting to appear. In the last day or two, he's been a little bit down, but that's football and he'll recover.
"He'll get the best treatment and a good operation, and we wish him well with that. In the meantime, it's time for Rob Elliot to step forward and fill his boots. He needs to step up and perform."
Krul's loss could hardly have come at a worse time with Newcastle sitting at the foot of the Premier League table without a win to their name and only three points to show from their opening eight fixtures.
McClaren could be forgiven for bemoaning his luck too after speaking to his keeper earlier in the day and being told he would be on the bench against the Kazakhs, only to then be asked to step in in place of Jasper Cillessen.
The Magpies' head coach said: "When that happened, people who have worked here for many years were saying, 'For some reason, it's always Newcastle.' Here, it just seems to be one disaster after another.
"But you have to get on with it. This is football, and this is what happens.
"I couldn't believe the text I got on Saturday evening. It was incredible because I'd just spoken to Tim earlier in the day to wish him luck, and he'd said he was on the bench and wouldn't be playing. I said, 'Well, at least you'll be fit for next week.'
"So to get that text didn't exactly make my night."
McClaren has, however, been boosted by the return to training of defenders Daryl Janmaat, Massadio Haidara and Paul Dummett and midfielder Jack Colback.