Wales are likely to miss the services of Taulupe Faletau at the start of the Six Nations 2018 campaign following a knee injury.
The 27-year-old sustained the blow while playing for his club Bath in the recently concluded European Champions Cup encounter against Toulon and was replaced in the 48th minute.
Bath have confirmed that Faletau has sustained a grade three medial knee ligament injury that is likely to keep him on the sidelines for 12 to 16 weeks. He is also expected to consult a specialist later this week to assess if a surgery is required.
"We are really disappointed for Taulupe," Bath rugby director Todd Blackadder said, in a statement released by the club.
"He's been in great form this season, so it's really unfortunate news.
"However, he is in great hands with the medical team, and we look forward to having him back on the pitch soon."
A 12-week rehabilitation period will keep Faletau out of Wales' Six Nations games against Scotland, England and Ireland.
Blackadder told reporters on Tuesday: "It's a serious one. We are looking at anywhere between 12 and 16 weeks.
"It's obviously a bit of a blow. I spoke to him after four big (autumn) games for Wales about how he was feeling both physically and mentally, and he was really good.
"It was just one of those things. A guy, sort of off the ball, dives sideways through his knee. These things happen."
Wales already have centre Jonathan Davies and flanker Sam Warburton both sidelined while Jake Ball is recovering from a dislocated shoulder.
Wales open their 2018 Six Nations campaign against Scotland at Principality Stadium on 3rd February next year.