Leicester back Jonah Holmes will be out until the early part of 2020 after partially tearing a medial collateral ligament in the Premiership defeat by Northampton last weekend.
The Wales international, 27, will be out for about six weeks and joins Telusa Veainu, Jordon Olowofela and Sam Aspland-Robinson on the sidelines.
Holmes has made nine appearances this season, scoring eight tries.
"It adds some pressure to us at a tough time," coach Geordan Murphy said.
"We're very disappointed for Jonah, he is a much valued member of this squad and it's a cruel blow for him given the form he is in for us.
"Since returning to the group part way through the pre-season programme, after spending the opening months of the summer with Wales, he has added a lot to this young group."
Wales handed Holmes the first of his three international caps in November 2018 against Tonga, and he most recently played against Ireland in a World Cup warm-up game in August.