Vikings quarterback J.J. McCarthy has torn meniscus in right knee

O’Connell said he wasn’t sure which play caused McCarthy’s injury. “Thinking back and having watched it a few more times, I’d just be speculating because there wasn’t a moment where it was noticeable,” he said.

The Vikings had planned a methodical course of development for McCarthy, making Sam Darnold the No. 1 quarterback and saying the rookie wouldn’t start until he showed he was ready. But McCarthy’s debut on Saturday stoked optimism for the fanbase, as he recovered from an early interception to throw two long touchdowns and convert several key third downs.

“We talk a lot about this development plan,” O’Connell said Monday. “A huge part of it is, these real game reps where there’s coaches on the sideline, it’s just them and the defense and the officials out there. I want to see him continue to progress, but clearly everybody can see the arm talent. I just love seeing him come right back after the interception and still be aggressive, still stay true to footwork, timing, rhythm, where his eyes should be. So there was a lot of positives with J.J.’s performance tonight, and a lot of areas where we’ll be able to hit the ground running when these guys are back.”

That work will have to continue off the field for now, as the Vikings learn more about how long they’ll be without the rookie. The injury is the Vikings’ second major loss at quarterback in the past 10 months, after Kirk Cousins’ torn Achilles last October; especially if McCarthy is out for most of the season, the injury could have implications for the Vikings’ transition plan at quarterback.

For now, they’ll move forward with Darnold, who went four-for-eight for 59 yards and a touchdown on Saturday, firmly in the top job. “My confidence in Sam is very, very high,” O’Connell said.