On Saturday, J.J. McCarthy showed the world the benefits of a rookie quarterback playing in preseason games.

In his first NFL action after up-and-down practice performances, the No. 10 overall pick came off the bench to throw 45- and 33-yard touchdowns against the Raiders. He sat down after reaching the 30 snaps the Vikings had scheduled for him.

On Tuesday, he showed the risks of a rookie quarterback playing in preseason games. The Vikings announced that the La Grange Park native, who reported soreness to the team on Monday, had torn his knee during the game. He’ll have surgery this week, and the results could range from a meniscus trim that allows him to return by the end of September to something more serious that could sideline him the rest of the season.

The Vikings await their doctor’s evaluation. “Certainly, what’s best for the long-term health of J.J.

McCarthy will be the priority,” coach Kevin O’Connell told reporters. “I don’t have that answer and really won’t be a part of determining that answer.” As the Bears debate whether to play their starters on Saturday at Soldier Field — the Bengals will bench theirs — they’ll have to weigh both extremes.

To keep Williams healthy, the Bears can claim, as they did last year, that their quarterback’s work during a joint practice is good enough. The Bears host the Bengals for practice Thursday afternoon at Halas Hall. The alternative to sitting Williams, though, is the jolt of excitement he provided .