The San Francisco 49ers certainly could’ve used Michael Crabtree on Sunday against the Seattle Seahawks, and there’s a chance Crabtree’s Achilles tear heals soon enough to face Seattle at home on Dec. 8. Chris Culliver won’t be back after tearing his ACL during training camp, and after two games it looks like the 49ers miss their nickel corner — perhaps not as much about Crabtree, but the void Culliver left is noticeable.

Nnamdi Asomugha SF 49ers training campThe 49ers weren’t quick to guarantee Nnandi Asomugha a spot after signing him, forcing the former All-Pro to win the nickel cornerback job in training camp over Tramaine Brock and Perrish Cox. Asomugha played well during the preseason, allowing one five-yard reception on four targets, making two strong tackles and even throwing in a couple quarterback hurries. But there was always a sense that the 49ers settled on Asomugha heading into this season — especially when they signed free agent cornerback Eric Wright, even though Wright was dealing with a DUI charge and an earlier trade the 49ers made to get Wright was voided.

When I asked Vic Fangio to assess Asomugha’s performance against Green Bay, the 49ers defensive coordinator said, “He had some good plays. He had some big plays for us on a couple third downs. He also missed a tackle or two there that hurt us. So, he had some good and some bad and we need to eliminate the missed tackles.”

The Packers attacked Asomugha throughout. Asomugha spent most of his snaps covering Jordy Nelson, who caught four passes on seven targets against him for 63 yards and a touchdown. However, as Fangio said, Asomugha stopped Nelson from making a deep catch on 3rd-and-3 and was defending James Jones when Aaron Rodgers threw an incomplete pass in his direction on 3rd-and-2. According to Pro Football Focus, Asomugha missed one tackle in Week 1.

If Asomugha “had some good and some bad” against the Packers, he was mostly bad against Seattle. Asomugha missed three tackles against the Seahawks, and while he allowed no receptions he was called for a 40-yard pass interference penalty on a long pass to Golden Tate. Tate never quite broke free from Asomugha’s coverage, but Asomugha never looked for or made a play on the ball. That was one of two devastating penalties during the drive where the Seahawks scored a touchdown to go ahead 19-3 (the other came four plays later when Aldon Smith committed a personal foul after a 15-yard pass on 3rd-and-28).

It’s not like Culliver was immune to getting flagged for PI — Culliver committed 11 penalties that resulted in 124 yards for the opposition last season (Culliver was penalized for the fourth-most penalty yards in the NFL among all players), including four pass interference calls. But in 16 regular season games, Culliver only missed four tackles — the same number Asomugha has in his first two games in Culliver’s spot. In case you’re wondering, Asomugha committed seven penalties (three PI) and missed seven tackles in 2012; he played 321 more snaps than Culliver last season.

But if it’s a sure-tackling corner they’re looking for, Wright probably isn’t the guy. He missed 14 tackles in 2011 with the Lions and 9 in 2012 with the Buccaneers. Wright can’t practice with the team for the first six weeks of the season anyway, since he’s on the Reserve/Non-Football Injury list. If Brock or Cox were the answer, they would’ve beat out Asomugha in August. Besides practice squad players like Darryl Morris or Michael Thomas (who the 49ers tried out a little as a slot corner during training camp), those are the 49ers’ only options.

The 49ers are in a tough spot. Their defense played well in the first half in Seattle, and they won despite Rodgers testing Asomugha a week earlier. However, Asomugha is clearly the weak link in the secondary both statistically (his PFF score of -5.1 includes a -3.8 score in coverage and a -1.8 score as a run defender) and based on who teams are targeting downfield. It’s inevitable that Andrew Luck and the Indianapolis Colts will go after him as often as they can on Sunday, and if Asomugha misses more tackles and/or surrenders more big plays, the 49ers may be forced to see if anyone else can do a better job replacing Culliver.