French side Bourgoin and Welsh team Cardiff Blues make up their pool and Frankie Sheehan, Munster's Ireland international hooker, said: "It will be tough.
"Leicester have been the most consistent team in Europe for the last four or five years and Cardiff finished last season very well, but hopefully we can get through it."
Sale Sharks, the new Premiership champions, were drawn in the same group as French giants Stade Francais, Italians Calvisano and Welsh team Ospreys.
European Cup draw:
Pool 1: Treviso (Italy), Perpignan (France), Wasps (England), Castres (France).
Pool 2: Edinburgh Gunners (Scotland), Agen (France), Gloucester (England), Leinster (Ireland).
Pool 3: Sale (England), Stade Francais (France), Calvisano (Italy), Ospreys (Wales).
Pool 4: Cardiff Blues (Wales), Bourgoin (France), Leicester (England), Munster (Ireland).
Pool 5: Ulster (Ireland), Toulouse (France), London Irish (England), Llanelli Scarlets (Wales).
Pool 6: Biarritz (France), Northampton Saints (England), Parma (Italy), Border Reivers (Scotland).