Lock Rowlands harm his shoulder, whilst flanker Lydiate suffered a damaged arm right through the 20-13 victory over Argentina remaining weekend.
“They’re each seeing consultants,” Wales head trainer Pivac mentioned.
“They’re each out of this sequence, and they are going to now not be again any time quickly. They’re each moderately severe accidents.
“Clearly, we want to suppose they are going to each be again at some degree right through the Six Nations.”
Whilst Rowlands and Lydiate start the restoration procedure, Scarlets back-row ahead Josh Macleod will get ready to make his Wales debut in opposition to Georgia on Saturday.
It will have took place remaining 12 months in opposition to Six Countries combatants Scotland, however he suffered a ruptured Achilles tendon in Wales’ first coaching consultation after he was once decided on.
Pivac added: “Any damage that takes you out of the primary alternative to play in your nation is huge, isn’t it?
“For that one (Achilles damage) I used to be status about two metres at the back of him, he simply speeded up from a status get started and it was once like any person had shot him with a gun.
“You heard the rupture, so it was once an unpleasant one.
“I be mindful announcing to him, regardless that, sooner than he left the lodge that he will have to move away with the information that this training staff had decided on him on his deserves.
“I instructed him, ‘Paintings laborious now and you’ll be more potent for it. While you come again, equipped you might be taking part in neatly, you’ll get every other alternative’.
“He has long gone away and labored very, very laborious on his recreation, and this is a credit score to him and the folks round him as a result of it’s all the time scientific people who do the unseen paintings and the energy and conditioning boys that lend a hand those guys get again.
“It’s only a excitement to peer him again at the taking part in box. He’s an attractive younger man and he works very, very laborious at his recreation.
“He’s an excessively bodily participant, and I believe the most important step going from membership to global is the physicality required, so it will be very fascinating to peer how that transfers for him.”