He comes in for Leinster incumbent Mike Ross who was ruled out with a hamstring tear suffered in their RaboDirect PRO12 final defeat to the Ospreys ten days ago.
Team manager Mick Kearney revealed that Ross had nearly made the side but was deemed not quite ready.
Kearney said: "Mike trained this morning and before we went out we were quite optimistic that he would come through the session," said manager Mick Kearney.
"He did the warm-up fine and when we went into team manoeuvres he just felt a bit of a twinge. The physios took him off and examined him and just felt it was more prudent to actually leave him off.
"Hamstrings, by nature, can take a while and you don't really know when they're going to be right, but I think we would be optimistic about next week. But probably the right thing to do was to pull him out this morning."
Fitzpatrick is not the only new face in the Irish team, with Munster flyer Simon Zebo also named for the clash.
The 22-year-old winger was the top tryscorer for the provinces last season and takes advantage of the absence of Tommy Bowe to start on the left wing.
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