SANTA CLARA -- Colin Kaepernick wants the 49ers to enter the playoffs on a six-game win streak, meaning they must triumph Sunday at Arizona even though they've already clinched a playoff berth.

"We have to keep our momentum going into the playoffs," Kaepernick said Thursday.

The 49ers (11-4) still don't know if they'll be the NFC's Nos. 1, 2, 5 or 6 seed. Sunday will clarify that situation, and it'll serve as a final chance to prove if their revitalized receiving corps is indeed a postseason threat.

The playoff-hopeful Cardinals (10-5) state they'll be facing a more dynamic offense with Michael Crabtree in the mix, but they're not convinced he's at full strength.

San Francisco 49ers Michael Crabtree (15) makes a catch against the St. Louis Rams in the fourth quarter at Candlestick Park in San Francisco, Calif., on
San Francisco 49ers Michael Crabtree (15) makes a catch against the St. Louis Rams in the fourth quarter at Candlestick Park in San Francisco, Calif., on Sunday, Dec. 1, 2013. The 49ers won, 23-13. (Josie Lepe/Bay Area News Group)

"He's slowly getting back into the groove, like he's trying to get back in game shape," Cardinals cornerback Patrick Peterson said on a conference call. "You can tell he doesn't look as comfortable as he did when he was healthy."

Crabtree, who torched Peterson and the Cardinals last season for four touchdowns in two games, is four games into his comeback from Achilles surgery. He notched his first 100-yard game Monday night as the 49ers beat the Atlanta Falcons 34-24 to secure at least a wild-card berth.

"It's good to see him back out there playing, because that is a hard injury to overcome," Cardinals coach Bruce Arians said. "I do not see the same guy, but he's getting really, really close."

"He looked really, really good Monday," Peterson added. "Hopefully he doesn't look good Sunday."

The Cardinals must win to keep alive their playoff chances, contingent also upon a loss by the New Orleans Saints (10-5) at home to the Tampa Bay Buccaneers (4-11).

Because Arizona touts the league's top-ranked run defense, that might force Kaepernick to excel through the air, and any postseason opponent's focus against the 49ers will be stopping their potent rushing attack. That, in turn, leads to the question: How well can Crabtree complement Anquan Boldin and Vernon Davis?

Greg Roman, the 49ers offensive coordinator, noted how Crabtree is only four games into his return and compared that to an exhibition-season worth of action "with no training camp."

Crabtree's contribution has been made more relevant by the uncertain status of Mario Manningham. After missing Monday's game with lingering knee soreness, Manningham took himself out of Thursday's warm-up drills and walked to a side field with a trainer.

Manningham made his season debut Nov. 10, and he had only one reception in the three games he overlapped with Crabtree's comeback.

Kaepernick said defenses are playing the 49ers more "honest" with Crabtree's presence. Arians and Peterson agreed, noting that Boldin and Davis have become tougher to defend as a byproduct.

For Boldin, this will be his first time playing in Arizona since the Cardinals traded him in 2010 to the Baltimore Ravens. To promote that return, a movie-like poster appeared on his Twitter feed on Christmas, titled "Boldin Returns To The Desert," with a list of his achievements since 2010. The image was posted by Boldin's personal public-relations staff, according to the 49ers.

Boldin, himself, downplayed a matchup with the Cardinals as "just another game" before the 49ers won 32-20 at Candlestick on Oct. 13. In that game, Boldin had just three catches for 28 yards, while Davis went off for eight receptions, 180 yards and two touchdowns.

"All three of those guys have big-play ability," Peterson said, "so (Crabtree's return) just made them that much more of a dynamic offense as far as dumping the ball off and passing the ball around."

Kaepernick anticipates facing a fast, physical Cardinals defense that's excelling with the same scheme since their last meeting.

Said Kaepernick: "We just have to go out and execute like we have been doing."

As a result, they have a third consecutive playoff trip to get ready for, and nowhere might that matter more than with their passing game, still ranked a lowly 31st at 179.1 yards per game.

For more on the 49ers, see Cam Inman's Hot Read blog at blogs.mercurynews.com/49ers. Follow him on Twitter at twitter.com/CamInman.

SUNDAY'S GAME

49ers (11-4) at Arizona
(10-5), 1:25 p.m. FOX