Farrell was substituted in the second half with an ankle injury first sustained tripping over television wiring warming up prior to kick-off while Vunipola also left the game early with a knee complaint.
But despite sitting out training on Tuesday, Saracens director of rugby Mark McCall was confident fly-half Farrell, who came off the bench in the third and decisive Test Down Under last summer, would start at Twickenham this Saturday, while Vunipola was waiting on results of scans.
"Mako has had some scans, but we expect news later in the week," said McCall. "Owen's fine and fine to play on Saturday.
"He clearly suffered a small sprained ankle, a slight ankle sprain, but Owen's fine and it's not a worry.
"That was the worst possible thing that could have happened ten minutes before the start of the match, what happened.
"He came into the changing room and his ankle had swollen straight away, it was big, and that's not ideal.
"But it kind of shows you his strength of character that he gets on with it and he plays okay.
"I thought he played well in the game so it didn't affect his performance."