The San Francisco 49ers officially announced the release of longtime starting linebacker Ahmad Brooks on Friday afternoon. He had been involved in a training camp and preseason battle with Eli Harold for the starting strong-side linebacker job. The move wasn't a complete shock for the rebuilding 49ers. Brooks is 10 years older than Harold and his salary cap figure of $6.15 million was significantly higher than Harold's figure of just over $823,000.

"Once we came to the conclusion that [Brooks] wasn't going to be part of our 53, we weren't going to keep him around to let him know nine days from now," Shanahan said. "We know there are a lot of teams that will be interested in him so we gave him that opportunity to go out and find them."

Shanahan went on to say that Eli Harold is now their starting strong-side linebacker and he feels good about the depth that remains at the position.

"He's a physical player," Shanahan said while describing Harold. "He can set the edge. I think he's got a lot more in him. I think he can continue to improve but I love the way he fights. I love the way he competes every day. He's a guy, to me, who was trying to be his best every day. I think there's a lot more to come. Usually, the guys who have that type of mentality, they usually get better, not worse."

Over his 11-year NFL career, Brooks has 370 tackles, 53.5 sacks, 30 passes defensed, three interceptions, and 12 forced fumbles. Brooks' 51.5 sacks with the 49ers rank third in team history behind just Bryant Young and Charles Haley, which impressed Shanahan. The 49ers head coach shared some of his thoughts about Brooks' history with the team and what it was like talking to him on Friday.

"I talked to Ahmad this morning," Shanahan said. "Yeah, Ahmad was great. To tell you the truth, it was real hard for me to do. I never knew Ahmad until I got here. I've had a lot of respect for him over his career and he's been great for me since I got here. Really enjoyed him as a person and when you have a guy who's meant to this organization, just looking it up, to be third in sacks all-time for the San Francisco 49ers, it's a pretty big deal. I think there's a pretty good history here. To be third all time, it shows the type of career Ahmad has had here.

"And I know some of the defenses he's been on, I'm going against, he's played on some real good defenses. I did think it was a bigger deal than usual. Ahmad handled it like a pro. He was great (while) talking to him and I wish him nothing but the best."

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Shanahan was asked if age played a factor in the 49ers' decision to release Brooks.

"Ahmad can still do things," Shanahan said. "I think everybody knows that and I think he's going to help somebody this year. It really comes down to the final 53. I'm starting to get a better feel for what that is now and it's taken me some time. It's taken [general manager John Lynch] and I some time because you've got to know what our group is like.

"It's really been nothing against Ahmad. It's, 'How are we going to get 53 guys on this team?' The right type of 53 guys. When you think of guys that might not be as good in Week 1 but you think they'll be ready in Week 3. What gives you the best chance to win in Week 1 and Week 8 and Week 16. You've got to play all that into account. It's rarely as simple as saying, 'Well, the starter versus the backup versus the third-string guy." It has to do with the overall 53."

Other Notes

Shanahan said C.J. Beathard would once again be the first quarterback off of the bench when Brian Hoyer and the first-team offense is done on Sunday. Beathard also backed up Hoyer during Saturday's loss to the Denver Broncos. Although, Shanahan stated that no one has won the backup quarterback job and Beathard will play before Matt Barkley on Sunday because Shanahan has seen the latter play in NFL games before. Barkley has been in the NFL since 2013.

Safety Jimmie Ward will not play against the Minnesota Vikings.

As Shanahan said on KNBR Friday morning, undrafted rookie guard Erik Magnuson is not a starter and people shouldn't read too much into occasionally seeing a backup in with the first-team units.