Newcastle striker Siem de Jong has suffered a collapsed lung and will be out of action for eight weeks.
The Netherlands international, 26, who signed from Ajax for £6m in the summer, had surgery on Thursday.
De Jong, who suffered the same problem in 2013, has been out of action with a torn thigh muscle but was close to a first-team return.
"After months of hard work getting back to full fitness, it is such bad luck to suffer another setback," he said.
"We are all hopeful that the surgery I have had will ensure I don't have any repeat of the condition in the future.
"It's very sad for me personally, especially since I was almost back in contention and feeling great.
"I'm sorry for my team-mates, the club and our fans that I'm not able to help the team for a little while longer.
"I am determined to come back stronger as soon as possible. Thank you to everyone for your support."