Farrell hobbled off in the 70th minute as Saracens edged London rivals Harlequins 36-24 after rolling his left foot while making a tackle, prompting him to cry out in pain and then sit in the dugout with ice strapped to the injury.
England’s captain damaged the same joint in the final stage of the Six Nations but was cleared to play against Ireland before facing Smith in the Gallagher Premiership a week later.
The fear now is that he may have done additional damage that could have wider implications for England and Saracens, who host the Ospreys in the knockout phase of the Heineken Champions Cup on Sunday week.
Farrell damaged both ankles in the 2021-22 season and his director of rugby Mark McCall said: “I’ve seen him in the changing room and he’s OK. We just need to see what the problem is and to what degree he’s aggravated it.
“It was a grade one strain before which is normally a seven-day turnaround, which he managed to do in the England week and play that game (Ireland).
“Whether or not it’s still a grade one, well see. If it’s more than that he won’t play. We certainly won’t play him if he’s not right.
“We want to make a good decision on it. It will be great to have him but if we don’t have him then we’ll get on with it.
“Until Owen went off he was great. All the good stuff in attack, he was at the centre of that. There were some great defensive interventions too.”
I've seen him in the changing room and he's OK. We just need to see what the problem is and to what degree he's aggravated it
Mark McCall on Owen Farrell's injury
Another head to head providing an international sub-plot was the clash between England number eights past and present.
Billy Vunipola won that particular battle by overshadowing Alex Dombrandt with a forceful display that saw him take the man of the match award as leaders Saracens claimed a bonus-point win that guaranteed a home play-off.
“Billy is just so determined. He’s in great physical condition and this is as good as I’ve seen him. You can see that on the field, he had a superb match,” McCall said.
“Billy’s got to do his talking on the field. That’s all he can do – play well. And he has been playing well.
“The way he dealt with the disappointment of not being in the Six Nations squad was unbelievable. He threw himself into helping our younger players.
“Sometimes that can be a frustrating experience for an international player but he’s responded really well.”
Smith started two of England’s Six Nations matches but was an unused replacement against Ireland.
The young pretender to Farrell’s playmaking throne was at the heart of Quins’ fightback against Saracens and head coach Tabai Matson insists he has dealt with his international disappointment well.
“I don’t think he will drop his head. One of the reasons he’s playing at that level is because he’s an assist magnet,” Matson said.
“He often is setting up a try for someone else or creating a line break for someone else. That’s why he’s one of the best.
“He created a lot of opportunities for others and got us around the field. It was a good performance from him. He rolled straight in after the Six Nations and has been delivering from day one.”