All three missed the Pool D wins over Namibia and Fiji but if they emerge from their foray back into training action unscathed they will be widely expected to start against their Celtic rivals.
Lydiate was struggling with ankle ligament trouble, Williams had a thigh strain and for Hook, he was sidelined with a shoulder injury.
"Dan, James and Shane have all been passed fit to train tomorrow," said WRU national medical performance manager Prav Mathema.
"Pending any adverse reaction we expect them all to be available for selection against Ireland this weekend.
"Gethin Jenkins and Sam Warburton are also both fit for selection following calf cramp experienced during the end of the Fiji fixture."
Meanwhile WRU boss Roger Lewis has moved quickly to insist boss Warren Gatland will not be departing for pastures new post World Cup.
All Blacks coach Graham Henry is due to depart at the conclusion of the tournament and the rugby rumour mill had linked Kiwi Gatland with a return home.
However Lewis insists the Wales chief - who's contract doesn't run out until 2015 - is going nowhere.
"Warren is a key pillar in our strategy and that's why I concluded negotiations with him in New Zealand in June last year," said Lewis.
"Warren signed with us just before the autumn internationals and it's an absolute watertight contract until the end of the 2015 World Cup.
"I have discussed with Warren what happens if he gets offers. I have made it clear we have made a huge commitment to him and he has to us.
"What's so exciting for the coaching team and backroom staff is the extraordinary group of young talented players it has at its disposal.
"The next four years promises to be so exciting for Welsh rugby and it certainly wouldn't make sense for Warren to leave us.
"It's hugely flattering for Warren and for the WRU that other countries are interested in him but it's hands-off our coach."