London Irish will play Cardiff Blues at The Arms Park on Saturday 6th December at 3:15pm live on BT Sport.
The reverse fixture the following week at Madejski Stadium will take place on Saturday 13th December at 3pm.
London Irish start the tournament this Sunday against Rovigo Delta at Madejski Stadium before taking on Grenoble away next Friday 24th October.
Fixtures for rounds 5 and 6 will be confirmed in due course.
For the full London Irish fixture list click here.