Jonathan Spratt, who spent the early part of the season playing at centre or full-back for Taranaki, provides new options behind the scrum and Samoan international lock Filipo Levi and Bridgend Ravens hooker Scott Baldwin will do the same up front.
Harlequins have added two England Under-20 players in winger Sebastien Stegmann, who has already played seven Premiership games this season, and lock Chris York.
Their last-eight opponents, Leinster, have added two of the 2007 Ireland Under-20 Grand Slam side in prop Jamie Hagan and out-half Kyle Tonetti, who played recently for the Ireland Sevens team.
ERC (European Rugby Cup) can confirm that the following players have been nominated by their clubs as their 'additional player(s)' for the knock-out stages of the 2008/09 Heineken Cup.
Additional Players - 2008/09 Heineken Cup Knock-Out Stages:
Date of Birth: 15/04/1987