"Following the result of extensive medical tests, it has emerged that Ireland hooker Richardt Strauss has been diagnosed with a heart condition and will be unavailable for the for selection for the remainder of the season," said a Leinster statement.
"The management are confident that the 27-year-old, who is set to undergo surgery this week, will make a full recovery and will provide him with the best care in his recovery."
To add to the worries of the three-time winners, and reigning Amlin Challenge Cup champions, new Australian recruit Lote Tuqiri has been ruled out of the game at the Liberty Stadium with a hamstring strain, while Brian O'Driscoll is only rated as 50/50 to recover from his calf injury.
O'Driscoll will continue to receive treatment from the medical team through to Friday's lunch time team announcement, which could include new signing Zane Kirchner for the first time. The Springbok full back linked up with his new team mates this week after completing his international obligations in the Rugby Championship.
Leinster's Round 2 clash against Castres Olympique in the RDS on Saturday, 19 October (3.40pm KO) is on course to be a sell out with more than 16,400 tickets now sold for the visit of the Top 14 champions.