Special teams ace and locker-room mentor Rock Cartwright is apparently leaving the Raiders for the 49ers, having agreed to a one-year contract pending a physical, the NFL Network first reported Thursday.

In a long expected move, the 49ers released veteran cornerback Shawntae Spencer, who made 72 starts in eight seasons in San Francisco but none last year. He was due to make $3.3 million in 2012.

In each of the past two seasons, Cartwright won the Raiders’ Commitment to Excellence Award for his leadership and work ethic.

His on-field impact for the 49ers’ likely will come on special teams, filling a void created Tuesday when Blake Costanzo left for the Chicago Bears. Cartwright, 32, also could be an option as a kickoff returner and a fullback. He had four carries for 45 yards last season, highlighted by a 35-yard run on a fake punt to secure a 25-20 win at Houston on Oct. 9.

The Washington Redskins selected Cartwright in the seventh round of the 2002 draft, when their national scout was current 49ers general manager Trent Baalke. Cartwright, who spent his first eight NFL seasons in Washington, did not return a call Thursday seeking comment.

At Saturday’s ceremony for his Commitment to Excellence Award, Cartwright told this newspaper of his plans: “I love it here. I would like to spend the rest of my career here. How long is that, who knows?”

As for the 49ers’ ongoing search to add wide receivers, former New York Giants star Mario Manningham visited Santa Clara on Thursday and then flew to meet with the St. Louis Rams, ESPN reported. The 49ers also have hosted two other free agent receivers, Brandon Lloyd and ex-Raider Chaz Schilens.

Ted Ginn Jr.’s chances of re-signing with the 49ers look bleak. He told the Detroit Free-Press he wants to be used more as a wide receiver than a return specialist.

Ginn had 19 receptions for 220 yards with no touchdowns last season, when he made three starts and otherwise lined up as the No. 3 receiver or split time as the No. 2 receiver.

Asked how the 49ers might have fared if he played in the NFC Championship game, Ginn told the Free-Press: “We’d have been in the Super Bowl.”

A knee injury kept Ginn out of the NFC Championship game overtime loss to the Giants, and Kyle Williams floundered as Ginn’s replacement by botching two punt returns.

For more on the 49ers, see Cam Inman’s Hot Read blog at blogs.mercurynews.com/49ers.