Leinster and Ireland prop, Jack McGrath has been ruled out for “the next few weeks” after picking up a knee injury during training last week.
The Champions Cup holders are set to begin their defence on October 12 in the RDS against Wasps with McGrath now in a race against time to be fit for the game.
Leinster are due to face Dragons and Edinburgh in the coming weeks before two massive clashes, back-to-back provincial derbies against Connacht (away) and Munster in the Aviva Stadium.
Head coach, Leo Cullen is hopeful that the 28-year-old will be fit for the Munster game.
However, the squad have been boosted with the return of a number of internationals. Johnny Sexton, Garry Ringrose, James Ryan, Josh van der Flier and Rob Kearney have yet to feature this season but may make their appearances against Dragons this weekend.