Harlequins have slipped to three successive defeats in all competitions but have not lost four in a row since January 2010.
Quins’ only win in their last four home games was 20-14 over Gloucester in the Heineken Cup on 14 January.
London Irish ended a three game losing streak with their 23-15 victory at home to Gloucester in the Anglo-Welsh Cup on Saturday. The Exiles’ solo win on the road in Aviva Premiership Rugby this season was 14-13 at Northampton in round three.
Harlequins have already beaten London Irish twice this season: 29-24 in the Premiership at Twickenham in September and 26-19 at Twickenham Stoop in the Anglo-Welsh Cup in October. The Exiles have not won at the Stoop since the Premiership semi-final in May 2009.