The Dutchman has suffered what is believed to be a serious groin tear.
It seems Siem de Jong is down on his luck at the moment.
The Newcastle United man suffered a collapsed lung at Ajax last season, which forced him to spend a lengthy spell on the sidelines.
And now it is feared the Dutchman will face no less than four months out of action with a torn groin.
De Jong suffered the injury in Newcastle training, meaning he missed out on the Netherlands' squad to face Italy (a game they lost 2-0).
The injury comes as a huge blow to both De Jong and boss Alan Pardew, who would likely have depended on the Dutchman to help his side find their touch in front of goal.
Only recently had De Jong said the following about aiding his side's pursuit for goals: "I think there are players who can score.
“We shouldn’t be talking about it all the time. If you talk about not scoring all the time, it gets into your head.
“Everybody wants to score – especially the attacking players. We shouldn’t worry about that too much.
“Manu [Riviere] and [Remy] Cabella are also new and also need a little bit of time. It’s always a little difficult at the start of the season when you fit in new players.
“You have to get used to each other - hopefully, we can get better in the coming weeks.”