Norwich City duo Jordan Hugill and Kenny McLean could be out for several months if they need surgery on respective shoulder and knee injuries.
Striker Hugill, 28, came off at half-time in Saturday's win at Middlesbrough and has damaged shoulder ligaments.
While Scotland midfielder McLean, also 28, has a torn knee cartilage and will see a specialist this week.
"He will be out for six weeks or if he needs surgery it could be four to five months," said head coach Daniel Farke.
On Hugill, who joined on a deal that could be worth £5m from West Ham in August, the Canaries boss added: "He may need surgery, so that will mean a long-term absence. But he's definitely out for three weeks."
Meanwhile, Norwich midfielder Todd Cantwell will be out for three weeks with a hip injury, while on-loan full-back Xavi Quintilla (also hip) may be sent back to parent club Villarreal for further examination.