The 24-year-old was operated on, with Leinster head coach Leo Cullen confirming that Ryan will be out for up to three months.
Ireland are due to play Italy at the Aviva on October 24th, followed by France in Paris the following weekend.
The matches were originally scheduled to be played in March, but were postponed due to the Covid-19 pandemic.
While Ryan may miss out on the final rounds of the Six Nations, he may be fit in time for this year's one-off tournament in which Ireland will play England, Wales and Fiji in the pool stages of the international series starting November 14th.
Following the pool stages, Ireland will play the correspondingly ranked team from the second pool in Dublin. The second pool includes France, Scotland, Italy and Japan.