Norwich defender Christoph Zimmermann is set to be sidelined for up to six weeks following knee surgery.
The Premier League newcomers confirmed Zimmermann had "sustained a medial meniscus tear in his left knee during the off-season", with the operation taking place last week.
The 26-year-old centre-back played a crucial role as the Canaries were promoted back to the top flight and on Tuesday it was announced the German has agreed terms on a new four-year deal.
A statement on the club websites read: "Norwich City can confirm that centre-back Christoph Zimmermann will miss the next 4-6 weeks of action after undergoing knee surgery.
"Zimmermann sustained a medial meniscus tear in his left knee during the off-season and had surgery in London last week.
"He is now back at the Colney Training Centre and working hard to get back to full fitness as soon as possible."
The loss of the German, signed from Borussia Dortmund II during the summer of 2017, is a setback for Daniel Farke's squad as they prepare for the Premier League opener at European champions Liverpool on August 9.
Norwich have moved to tie several key members of last season's Championship winning squad on new deals, including playmaker Emi Buendia and striker Teemu Pukki.
Teenage full-back Max Aarons is also said to be in line for an improved contract, the 19-year-old having been linked with several other Premier League clubs this summer.
Norwich have so far brought in Swiss forward Josip Drmic after he left Borussia Monchengladbach, while Schalke goalkeeper Ralf Fahrmann and Manchester City winger Patrick Roberts having joined on season-long loan deals.