He is now hoping to make his first appearance since his switch from Wigan Warriors in the warm-up match against fellow London side Harlequins at Harpenden.
Farrell had clinched his place at inside centre with his performance in a Probables v Possibles match in mid-week but also picked up the injury which led to Saracens head coach Steve Diamond deciding not to take any chances with his expensive acquisition.
Diamond said: "Andy played the full match in mid-week but unfortunately had his toe stepped on. It's just a bit sore.
"I would rather have him able to take part in a full week's training next week and be available for the weekend."