Farrell, 23, has struggled for fitness and form and was replaced by George Ford at fly-half for England during the autumn internationals.
Leinster’s opponents in next weekend’s Champions Cup action, Castres, were on the wrong end of a 49-13 hammering from Stade Francais, who went clear atop the French Top 14 on an emotional day in Paris.
Tries from Fiji wing Waisea Nayacalevu, Jonathan Danty, a hat-trick from captain Sergio Parisse and a penalty try ensured Stade took the maximum five points form the encounter.
Toulon — who face Ulster at the Stade Felix Mayol on Saturday — scored four tries as they beat Johnny Sexton’s Racing Metro 32-23. Toulon were inspired by fly-half and inside centre Juan Martin Hernandez and Matt Giteau, who were starting together for the first time.