Saints must topple the Irish province to take command of Pool One ahead of the return fixture at the Aviva Stadium next Saturday.
George North, Northampton's giant Wales wing, is braced for a ferocious challenge over the coming eight days.
"We have two very difficult games against Leinster to overcome," he said.
"We could and should have won in Castres in the last round and that defeat has made our task all the more difficult.
"As former winners, Leinster have proven themselves on the European stage time after time.
"They have a very physical pack and some superb backs, so we are expecting two high-paced and very tough games."
The clash is a re-run of the memorable 2011 final when Leinster fought back from 22-6 down to take the trophy in a classic Millennium Stadium final.
Saints are looking for revenge against the unbeaten Pool One leaders but are missing George Pisi, Ben Foden, Jamie Elliott, James Wilson and Kahn Fotuali'i through a mixture of suspension and injury.
Fly-half Stephen Myler insists their absence is no excuse for Northampton.
"We may need to alter a few things but it's something we feel capable of and you have to deal with it," Myler said.
"We feel we're in a strong position and that we've got players who can come in and are doing a good job. We know what a quality side Leinster are. We're really excited. It's a good test for us."
Harlequins travel to Racing Metro in a late kick-off looking to move off the bottom of Pool Four.