Andrea Masi, the Wasps and Italy centre, will be sidelined for up to five months after undergoing knee surgery.
The 32-year-old sustained the injury against Sale Sharks on September 20, damaging both his posterior and medial cruciate ligaments.
Masi has no chance of playing in the Azzurri's autumn internationals and may also be considered a doubt for the 2014 RBS 6 Nations.
A Wasps statement said: " London Wasps back Andrea Masi this week underwent surgery on the knee injury he suffered in the game against Sale Sharks.
"Masi suffered damage to both his MCL and PCL and will be on the sidelines for a period that is estimated to be between 16 and 20 weeks."