Kyle Shanahan: There is a ‘real good chance’ 49ers rookie LB Fred Warner starts against the Vikings

You don't typically see too many starters play in preseason finales. That wasn't the case for San Francisco 49ers linebacker Reuben Foster on Thursday night. He played in three series against the Los Angeles Chargers.

Foster was in the game because he won't have an opportunity to get on the football field again until the 49ers visit the Kansas City Chiefs on September 23. He will be serving a two-game suspension for violations of the league's policies on substances of abuse and personal conduct.

Seeing Foster suited up on Thursday night was a bit of a shock. The linebacker was just five days removed from a concussion he sustained against the Indianapolis Colts. He was out of the concussion protocol on Wednesday.

"Once he got out of the protocol and felt good, that's what we planned on doing (playing him in the game) all along as long as he was healthy," head coach Kyle Shanahan said following Thursday's 23-21 loss.

Who will fill in for Foster during his time off? All signs are pointing toward rookie linebacker Fred Warner, who did not play against the Chargers. It was a strong indication that he will be the Week 1 starter.

"I think there's a real good chance (Warner will start), but we wanted to see the other guys tonight," Shanahan said. "Brock (Coyle) is still in the mix, and we'll see how Malcolm (Smith) ends up playing out because Malcolm has been battling through some stuff, but he stayed healthy last week. It's going to be one of those guys."

Warner had an impressive offseason and had shown flashes during the preseason before sitting out Thursday's game. He was in street clothes on the sideline while watching Foster, Coyle, and the others face Los Angeles.

"They told me that I would sit this game," Warner told reporters in the locker room after the loss. "I guess that means that they saw enough and maybe they need to see some other guys out there. Just making sure I'm healthy going into the year is the biggest thing I'm worried about."

The next time Warner suits up, he will likely be going up against quarterback Kirk Cousins and the Minnesota Vikings offense in the regular season opener. The team has already started to do its homework on Minnesota.

"Kirk Cousins is an outstanding quarterback," Warner said. "This is his first year in that system or on that team. Watching film from the preseason, he has a lot of ability, and they're going to have a good running game now that they have (running back) Dalvin Cook back. I'm sure we'll be prepared when the time comes for that."

The 49ers and Vikings open the season on Sunday, September 9 at U.S. Bank Stadium.