But scans revealed the fly-half had not sustained any serious damage and he was back in the team as Saracens booked their spot in the European Cup final with victory over Clermont Auvergne last weekend - the Englishman crossing the whitewash before halftime.
Farrell did not assume kicking duties in the match however with Alex Goode taking on the mantle - a move that was repeated in Saturday's 44-20 win over Worcester Warriors.
But McCall expects to see Farrell, who was part of the Lions' series-winning 41-16 victory over Australia after coming off the bench in the third Test, back on full duties in time for next weekend's game at Leicester Tigers.
"Owen's foot is fine, but it's just place-kicking that seems to aggravate it a small bit," said McCall. "So we're just giving him a week or so without having to do that again. We're very confident he'll be place-kicking by the middle of next week.
"It was just a case of getting Owen's place-kicking foot right. But as you saw he played pretty well apart from that."
McCall also moved to calm fears over fellow Lion Mako Vunipola who was taken off after just seven minutes with a hamstring injury.
"Mako just tightened up his hamstring, and with the games we've got coming up we got him off the pitch as soon as we could," added McCall.
"Hamstrings are too hard to tell, he just had an awareness and we thought we'd get him off the pitch. We'll have more news on that in the next few days."