Must happen/can't happen against Cardinals

SANTA CLARA, Calif. -- Here is a look at what the San Francisco 49ers must do and can't do Sunday at Arizona:

Must happen: Get the ball to Vernon Davis. When the 49ers beat Arizona 32-20 in October, Davis took over. He had one of the great all-time days by a tight end in NFL history. He had eight catches for 180 yards. The Cardinals have struggled covering the tight end this season. The 49ers have to exploit it, especially after Davis was held catch-less against Atlanta. It was the first time he didn’t have a catch all season.

Can't happen: The 49ers can’t let the Cardinals pass at will against them. The 49ers have been good all season on defense. But the pass defense struggled against the Falcons. Matt Ryan completed 37 passes and threw for 348 yards. The Cardinals can be dangerous in the passing game. If Carson Palmer gets in a groove with receivers Larry Fitzgerald and Michael Floyd, they can easily stay in this game.