Ulster captain Rory Best has been ruled out of Friday's Guinness Pro14 game against Glasgow Warriors.
The hooker suffered an ankle ligament injury in Saturday's Champions Cup clash against Leinster.
Ulster suffered a heartbreaking 21-18 defeat in the thrilling quarter-final game.
Leinster were also hit on the injury front with back row Dan Leavy suffering a "complex" knee injury.
In a cruel blow to both Leinster and Ireland, the injury is set to rule Leavy out until after the World Cup later this year.
The 24-year-old had just recovered from a calf-injury that forced him to miss the Six Nations.
Munster also have injury problems, with head coach Johann van Graan saying Joey Carbery's hamstring injury is "a big concern".
Carbery started in Munster's hard-fought Champions Cup quarter-final win over Edinburgh on Saturday but was forced off after 35 minutes.
"I’m not going to put a timeframe on it," said van Grann when asked about a return-date for Carbery.
"He was out six weeks the previous time [with his last hamstring injury], it is difficult to say at this stage because it is a hamstring, whether it’s worse or it’s less, so we will just take it from day to day… but I can say he will definitely not be ready for this weekend.”