How Jauan Jennings' absence will affect the 49ers against the Cardinals

This isn't what the 49ers needed.

San Francisco 49ers wide receiver Jauan Jennings (15). | Stephen Lew-Imagn Images

This is a tough blow.

The 49ers won't have their No. 1 wide receiver this afternoon when they face the Arizona Cardinals. That's because Jauan Jennings has been ruled out for Week 3 with ankle and shoulder injuries, according to ESPN's Adam Schefter.

Jennings did not participate in any practices this week, and yet the 49ers still listed him as questionable for today's game, which means they thought he'd be a game-time decision. Apparently, Jennings knew before he even reached the stadium that he's not ready to play.

Last week, Jennings played through his shoulder injury against the Saints and had 89 yards and a touchdown -- he looked perfectly healthy despite missing practice on Wednesday and Thursday. However, on Friday, he was a limited participant, which indicated that he would, in fact, play in New Orleans. This week, Jennings was not limited on Friday -- he simply did not participate, which indicated that he would not play in the home opener. The signs were there.

So what does Jennings' absence mean for the 49ers?

San Francisco 49ers wide receiver Jauan Jennings (15). | Stephen Lew-Imagn Images

For starters, it means that the 49ers won't have four of their best players -- Jennings, Brock Purdy, George Kittle and Brandon Aiyuk. In their places, the 49ers will start Mac Jones, Ricky Pearsall, Kendrick Bourne and Luke Farrell. We'll also see backup tight end Jake Tonges, and a whole lot of starting running back Christian McCaffrey. So don't expect the 49ers to score a ton of points against the Cardinals.

Fortunately for the 49ers, the Cardinals won't have two starting cornerbacks -- Garrett Williams and Will Johnson. Still, the 49ers will have just one starting-caliber wide receiver, and that's Pearsall. Which means the Cardinals can bracket him with two defenders, load the box to stop McCaffrey and force Mac Jones to throw to someone else.

Expect Jones to spread the ball around and hand it off to McCaffrey even if he's not ripping off big gains. Because the 49ers don't need to win this game with their offense -- they just have to not lose it. Their defense can win the game for them, because the Cardinals' offense is anemic. Their offensive line is no good, their wide receivers are nothing special and their quarterback, Kyler Murray, still plays like a rookie.

Both teams want to run the ball more than they pass it. Both teams have good run defenses. This should be a low-scoring field-goal fest. The team that makes the fewest mistakes will win.