The San Francisco 49ers traded linebacker Eli Harold to the Detroit Lions on Thursday. He spent the past three seasons in San Francisco after the team made him a third-round draft pick in 2015.

After Thursday's practice, head coach Kyle Shanahan discussed the reasoning behind the trade. He would have loved to have kept Harold on the roster, but the team had to make some tough decisions. It wasn't until Shanahan and the coaching staff started to look at what the 53-man roster might look like that the 49ers made the decision to trade Harold.

"It was a tough decision," Shanahan said. "Love Eli. It's been great getting to know him over the last year. But as this week went, just looking at how our final 53 is going to work out, I won't say it was just about Eli. It has a lot to do with how we think we're going to use people on game day, who's going to be up between defensive lineman, outside linebackers, inside linebackers. All three of those positions kind of play together.

"We had some numbers issues at certain spots, and we kind of saw how it was probably going to go. We wanted to do what was best for Eli, best for this organization, and make that decision now."

The 49ers have several players capable of playing at the SAM linebacker spot.

"There's so many different ways we can go here in the next 10 days," Shanahan said.

Shanahan was asked about rookie linebacker Fred Warner and the potential of moving him outside. Warner has only been practicing at inside linebacker, according to Shanahan.

"I think every guy on our roster who is listed as an inside linebacker is capable of playing outside linebacker," Shanahan said. "It just depends how you want to treat that position, the (opposing) offense treats it."

With Harold gone, Mark Nzeocha and Pita Taumoepenu took snaps at the SAM linebacker spot during Thursday's practice. Dekoda Watson continued to work at LEO while Fred Warner played inside linebacker.

Nzeocha will start at SAM against the Colts, according to Shanahan.

Offensive lineman Garry Gilliam remains in the concussion protocol and, as of right now, has been ruled out for Saturday's game against the Indianapolis Colts.

No decision has been made on cornerback K'Waun Williams (ankle) yet. He is questionable.

Defensive end Arik Armstead (hamstring), defensive lineman Solomon Thomas (concussion), and linebacker Malcolm Smith (hamstring) are expected to play.

Cornerback Richard Sherman (hamstring) is also expected to play.

"We're playing [Sherman] with the starters and we'd like the starters to play the first half," Shanahan said. "Like I said earlier in the week, it could be less, it could be a little bit more. I'd like to keep Richard on the same plan. He hasn't been out as much as everyone so we'll see how it goes. We'll monitor his reps.

"If it's a ton of reps, you never know how long two quarters can go, but hopefully he gets enough where he feels comfortable."

Starters typically do not play during the final exhibition game. Shanahan would not promise anything when it comes to Sherman. The two will talk after Saturday's game and discuss if the cornerback feels more work is needed. The 49ers are scheduled to play the Los Angeles Chargers at Levi's Stadium on Thursday, August 30.

"Based off of how [Saturday] goes and how practice goes next week, I'll talk to him and see how much he thinks he needs versus [the Chargers]," Shanahan said.