Bath have confirmed that England flanker Sam Underhill suffered an ankle ligament injury during last Sunday's Gallagher Premiership game against Leicester.
The west country club say "further detail around his expected return" will be provided after he is reviewed by a specialist.
It is understood that Underhill could be sidelined for at least four weeks, giving England head coach Eddie Jones a fitness concern ahead of his team's opening Guinness Six Nations games against Ireland and France early next month.
Underhill, 22, produced outstanding performances for England during this season's autumn Tests, most notably in the one-point defeat against world champions New Zealand.
He has won nine caps and quickly become a key player for Jones.
Bath, meanwhile, say that forward Matt Garvey faces around three months out after breaking his ankle during the Leicester match.
"Bath Rugby can confirm that Matt Garvey and Sam Underhill are going to be out of action following injuries sustained in the win against Leicester Tigers on Sunday," the club said in a statement on its official website.
"Garvey suffered a fracture to his ankle and is expected to need surgery, which will keep him out for around three months.
"Underhill sustained ligament damage to his ankle, and further detail around his expected return will be provided after his specialist review."
