The 30-year-old was replaced in the first half of his side’s victory over the Dragons at Rodney Parade.
The worst-case scenario for the Lydiate according to defence coach Brad Davis, is if he should need an operation, leaving him out of action anywhere from 12 to 16 weeks.
“We’ll know a lot more when he has had his scan and the medics can plan the best way forward for him,” Davis said.
“Hopefully it is not as serious as it could be. It’s absolutely gutting for him because since he’s come back he’s been a rock in the back row.”
“He gives you that physicality that you need, especially without the ball, so he is definitely going to be a loss for us.”
Lydiate is just the latest injury concern for Gatland, with Hallam Amos also potentially about to miss out, having injured his ankle for the Dragons on Boxing Day.
Gatland has also had a number of back row concerns in the lead up to the tournament.
Flanker Sam Warburton has already been ruled out for the remainder of the season and number eight Taulupe Faletau looks likely to miss the start of the campaign.
Wales kick off their campaign on the 3rd of February in Cardiff against a strong Scottish outfit.
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