Wales head coach Warren Gatland says that prop Samson Lee's World Cup prospects are "50-50" after he was injured during last Saturday's RBS 6 Nations victory over Ireland.
Gatland has confirmed that Lee, who was carried off just 14 minutes into the Ireland game, suffered a full rupture of his Achilles.
Ospreys prop Aaron Jarvis will replace him for next Saturday's Six Nations appointment with Italy in Rome, with loosehead Rob Evans taking over from Gethin Jenkins, who has a hamstring problem.
Gatland said: "We were hoping he (Lee) was going to have surgery on Monday, but there was too much swelling, and it has been put back a week.
"He is a 50-50 chance for the World Cup, but we are confident he has enough time to get back and be available for the World Cup.
"If things go well, he will not be far away."
Evans and Jarvis will line up against Italy, while there are call-ups on the bench for hooker Ken Owens, props Rhys Gill and Scott Andrews and scrum-half Gareth Davies, with Mike Phillips missing out.
Owens features among the substitutes instead of Gloucester hooker Richard Hibbard, who had been following return-to-play protocols after taking a blow to his head during the Ireland game.
Saracens forward Gill, meanwhile, gains a match-day place after only joining the squad for training on Monday, while Davies - a livewire operator and consistent try-scorer for the Scarlets - gets his chance instead of the hugely-experienced Phillips.
In terms of the starting line-up, it will be Evans' full Wales debut after he went on as a replacement for Jenkins at half-time last Saturday, with Jarvis continuing instead of Lee.
Wales will head to the Stadio Olimpico lying third in the Six Nations table behind England and Ireland on points difference.
A comprehensive victory over Italy, though, would turn up the heat on their title rivals, with Ireland tackling Scotland at Murrayfield next Saturday, followed by England hosting France at Twickenham.
Gatland added: "It was great to get the result we wanted in front of our home supporters last weekend and to give us a chance going into the last round of action.
"Obviously, it's disappointing for Gethin and Samson, but Rob and Aaron stepped up well last weekend and we expect the same on Saturday.
"The challenge to us is to go to Italy and win, and try to win by a significant margin, but we know that's an extremely tough ask and the first job will be to simply get the result.
"Italy build their confidence around the scrum and lineout drive, and that is an area we are going to have to compete strongly in at the start of the match."
Wales have won five of their previous seven Six Nations visits to Rome, highlighted by a 38-8 victory in 2005.
And they are going to need something similar - if not better - if they are to realistically have a chance of securing their third Six Nations title in four years.
It seems a bit like wringing a dirty mop out on the fire that's just warmed the entire house but after the glow of Cardiff it all comes down to the maths. The Calcutta Cup match swung along lustily but it too added not so much to the romance of a hard game well fought, but to the sums. The scoreboard has always demanded the ability to count. Now we must subtract.
First of all it has to be said that Wales were magnificent, one of the greatest defensive displays ever seen in international rugby, to make 288 tackles in a game of rugby may mean questions are asked of Ireland in attack. But, credit Sam Warburton and Wales, their defence was simply heroic.