"This is how I look at it: In this league, people - and I'm talking about fans, critics, personnel people upstairs - they're quick to label people as far as, 'They're old, they've lost a step,"' said Spikes, an 11-year veteran who just cemented a starting job with his fourth NFL team after just two months in San Francisco.

"If a guy's injured, 'Oh, he can't do this any more,"' Spikes said. "I don't look at it that way. This is something I believe, playing the game for so long. As a premier player, if you're healthy, you're that much better than everybody else. Even if you do get hurt and you're a step slow, you're still that much better than everybody else."

Spikes was injured in 2005 and 2006 when he was with Buffalo, and his feelings were bruised when the Eagles dropped him last March after one impressive season with the club. But Spikes still sees himself as an elite NFL linebacker, no matter what team is lucky enough to employ him - and his early success with the 49ers suggests he's correct.

Spikes is playing alongside rookie of the year Patrick Willis in an innovative San Francisco defense that sometimes leaves those two linebackers on the field all by themselves with five defensive backs and four linemen. Spikes has two interceptions in the 49ers' last two games, and his veteran work ethic has inspired his teammates even while San Francisco stumbles to a 2-3 start.

When the Eagles visit Candlestick Park on Sunday, he intends to show his good friend Westbrook and his former teammates what they're missing.

"I hate moving, and I thought my time stay would be longer there in Philly," Spikes said of his single year with the Eagles, who credited him with 139 tackles in his only season with the club before releasing him in early March to save $5 million against the salary cap.

Eagles coach Andy Reid's assessment of Spikes on Wednesday was brief and full of platitudes such as, "We loved having him here," and, "He loves to play the game."

Spikes has stronger feelings about Philadelphia's decision to let him go, though he keeps his comments civil - quite an achievement for a player known to do computer research to improve his trash talk.

"Whatever I know (about the Eagles), I'm going to express to our guys, especially about personnel," he said. "Just let them know that these are some of the things that I remember, that they like to do."

Spikes started his career in the anonymity of a perennially losing team in Cincinnati, but he made the Pro Bowl twice in Buffalo. He was traded to the Eagles before last season, but the club got rid of him two months after he ended a highly productive year with a torn rotator cuff.

Spikes signed with the 49ers in early August after a protracted courtship during which he entertained offers from several teams, waiting for the most lucrative deal with the best team possible. Spikes decided he wanted to be in an NFL camp by Aug. 12 to be fully prepared for the season, and he joined San Francisco two days before his goal.

The 49ers needed Spikes just as much as he needed them. Longtime leading tackler Derek Smith had been dumped $2 million on the salary cap, but hadn't really been replaced.

"People have made me feel comfortable ever since I got here, and I'm glad I made the right decision," Spikes said. "It's great to be on an up-and-coming team that expects to be in the playoffs, and we're working hard to be worthy of that."

Coach Mike Nolan wasn't completely sold on veterans Jeff Ulbrich or Brandon Moore, who both attempted to fill Smith's spot early in training camp. The 49ers also tried newcomer Dontarrious Thomas and seventh-round pick Larry Grant, but nobody provided the combination of athleticism and veteran smarts that Nolan hoped to put next to Willis, the defense's centerpiece.

Spikes got off to a weird start in his first regular-season game in San Francisco, fumbling a short kickoff that unexpectedly went to him. He shook off that early blunder with several weeks of consistent effort, gradually taking playing time away from Ulbrich until last week's loss to New England, when Spikes barely left the field.

"He's doing an outstanding job for us," Nolan said. "He's a veteran leader who's done a very good job of filling the role we needed to be filled. He's been a great signing."

Notes: Six players sat out of Wednesday's practice, including LB Roderick Green (stomach virus), LT Jonas Jennings (shoulder), LB Manny Lawson (hamstring) and S Michael Lewis (elbow). Lewis definitely will play Sunday, while Nolan is cautiously optimistic Lawson and Jennings could return. RB Frank Gore and CB Walt Harris also sat out, but aren't injured.