Paddy Jackson was named in the summer tour squad on Monday but was unable to train at the Ireland mini camp which took place in Dublin this week.
The injury will require rest and recuperation for Jackson to start next season fully fit. Ian Madigan has been confirmed as his replacement on the tour.
Speaking to U105 at the Ireland squad's reception in Stormont, Jackson said: "It came as a bit of a shock because the initial scan didn't show up that I had the stress fracture.
"It was a bit of a shock on the way home yesterday. I just went to get it injected but it showed up with bad news, so yeah it's a frustrating end to the season."
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