Djourou was substituted during Hamburg's Bundesliga relegation play-off second leg with Greuther Furth following a fall in the 31st minute of play at the Trolli Arena.
The former Arsenal man was taken off on a stretcher and Hamburg sporting director Oliver Kreuzer has confirmed the severity of his injury.
"The latest on Johan Djourou is that he has damaged a vertebra in his neck," Kreuzer said. "That's all we know at present."
Should Djourou be unable to recover in time for the World Cup then Wolfsburg centre-back Timm Klose, who is on the standby list, will be expected to take his place in the 23-man squad.
Switzerland have been drawn in Group E for the World Cup and start their campaign against Ecuador on June 15 before taking on France and Honduras.
