Ireland fly-half Johnny Sexton has been sidelined with a hamstring injury less than three weeks before the Six Nations game against Italy.
Leinster boss Leo Cullen said on Friday that Sexton's early substitution in the win over Dragons was "a precaution".
However, the Pro14 champions revealed on Monday that Sexton will miss their match on Saturday with a 'minor hamstring injury'.
Ireland host host Italy on 24 October and then meet France a week later.
Andy Farrell's side are four points behind leaders England and second-placed France but with a game in hand.
Ireland will then be involved in four games in the new international tournament in November and early December when their opponents will include Wales, England and Georgia.