SANTA CLARA – Early in the third quarter Sunday, Frank Gore took a handoff through the middle of the Cardinals' defense, picked up terrific blocks by guard Mike Iupati and wide receiver Michael Crabtree and scooted into the end zone for a 37-yard touchdown.

The 49ers led 19-7, and the offense appeared to be in excellent position to do what it does best: Grind away at the opposing defense and game clock with its big offensive line and running game.

It didn't happen that way. Gore carried the ball only two more times the rest of the game and wasn't on the field for the team's final two snaps.

On Monday, coach Jim Harbaugh explained why.

"He's got some things," Harbaugh finally said after prodding. "He's not 100 percent. We have other backs that got carries in the second half."

Harbaugh did not divulge what is bothering Gore, the team's workhorse running back since 2006, and Gore was not on the 49ers' injury report in the week leading up to the game.

Gore has dealt with sprains to both ankles this season – they occurred in Week 3 and Week 9 – and he suffered a sprained knee early in a Week 10 win against the Giants.

That injury coincided with a notable dip in his production.

Before that game, Gore had rushed for 100 yards or more in five consecutive games. He left the Giants game with six carries for zero yards and hasn't reached the century mark since. Sunday's touchdown was his first in the last five games.

The injury also appears to have influenced the 49ers' offensive game plans.

Before Week 10 against the Giants, the 49ers had been a run-heavy team. Prior to that game, they attempted 246 runs against 228 passes.

In the five games since, the ratio has flipped. The 49ers have run 145 times and called 174 pass plays.

Sunday's loss in Arizona had the most lopsided ratio of the season. Counting the five times that Alex Smith was sacked, the 49ers attempted 42 passes against only 21 carries.

After Gore's touchdown at the 12:24 mark in the third quarter, the 49ers ran the ball four more times – two by Gore and two by backup Kendall Hunter.

Gore and Hunter appeared to alternate carries. Gore gained eight yards on the game's first play, then headed to the 49ers' bench, while Hunter entered on second down.

Hunter also was on the field for the 49ers' final two snaps. The 49ers needed a yard for a first down, and they unsuccessfully tried to throw for it on both third and fourth down. Smith's last attempt went through the hands of a diving Hunter.

Gore and his teammates will get an extra day to rest this week. They host the Steelers on Monday and won't begin practicing for that game until Thursday.

Meanwhile, Harbaugh didn't use Gore's lack of carries as an excuse. Instead, he said the team would have to get together and fix offensive problems – primarily an inability to score touchdowns in the red zone – this week.

He also pointed out that the schedule won't get any easier. The 49ers, who won the NFC West last week, will play two more games against division opponents on the road to close out the season.

"You're the hunted now," Harbaugh said. "You're not the hunter as much. You've got a target on your back. People want to beat you."

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