Mathieu Raynal of France has been forced to withdraw from his Europrean Cup match and has been replaced by Neil Paterson of Scotland.
Catalan Raynal was to have refereed the Pool 3 match at the Stoop between Harlequins and Connacht on Saturday.
Paterson is Scotland's leading referee with experience in Tests, IRB Junior World Championship, Heineken Cup, Amlin Challenge Cup, Top 14 and Rabo Direct, apart from the Scottish Premiership.
The rest of the team of match officials is unchanged:
Harlequins vs Connacht at The Stoop
Referee: Neil Paterson (Scotland)
Assistant referees: Jean-Luc Rebollal (France), Mourad Zitouni (France)
Television match official: John Sheehan (Ireland)
Timekeeper: Vincent Azoulay (France)
Citing commissioner: Jean-Etienne Bernard (France)
Assessor: Bob Ockenden (England)