Thomas was being checked over by medical staff on Tuesday morning before caretaker coach Scott Johnson finalised his team to travel to Lansdowne Road.
He was rushed to hospital in Bridgend on Sunday evening complaining of a migraine and temporary paralysis on his left side.
"I thought I was going to die. I thought I was having a heart attack," said Thomas, who had earlier appeared on the BBC Wales programme 'Scrum V', defending the actions of his players in the lead up to Mike Ruddock's dramatic resignation.
It is not clear whether Thomas will be fit to face Ireland, but Jones feels it is important that such a talismanic figure makes the starting line-up.
"Gareth's a superb leader and a great guy and we wish him all the best," said Jones.
"He is our last line of defence so we want him out there playing. We hope he makes it but at the moment it's a case of having to wait and see.
"Our fingers are crossed that he will be all right."
If Thomas does not play there is a possibility that Gavin Henson could make a dramatic return to the fold.
Henson is back training with the squad after coming through his first game for seven weeks on Friday, when he started for the Ospreys against the Borders at full-back.