Mako Vunipola will miss England's autumn Test series following his calf strain.
The Saracens' loosehead prop will be sidelined for six weeks, with lock Nick Isiekwe also ruled out for two months due to an ankle concern.
"Mako's got a calf injury, so it looks like it's going to be around six weeks," said Saracens' rugby director Mark McCall. "It's a tear in his calf, it doesn't require surgery.
"Nick (Isiekwe) will be around eight weeks, it's a syndesmosis injury of his ankle.
"That doesn't require surgery either, and it will be eight weeks."
Vunipola becomes England's fourth loosehead missing ahead of the autumn: Joe Marler has retired from Test rugby, while Leicester's Ellis Genge, Bath's Beno Obano and Wasps' Matt Mullan are all sidelined with long-term knee trouble.