Northampton Saints hooker Mike Haywood could miss the rest of the season after suffering a "significant" knee injury.
The 27-year-old was forced off in their Premiership Cup defeat by Gloucester on Friday, his 200th Saints appearance.
"He really unfortunately sustained a freak injury where a guy fell on him and basically minced his knee," boss Chris Boyd told BBC Radio Northampton.
Meanwhile, England flanker James Haskell will be out for up to 10 weeks after having an operation on his ankle.
"Right from the time that he came to us that ankle's just been grumbling away," said director of rugby Boyd.
"It's more wear and tear than an acute situation but it's just progressively got worse."
Winger Tom Collins will also need surgery on a fractured eye socket, keeping him out for as long as six weeks, and taking Northampton's injury list up to 12 players - with another four away on international duty.