The San Francisco 49ers have needed an offensive lineman to step up at guard and an undrafted rookie is doing just that through two preseason games.

The 49ers have committed to Brock Purdy with a big extension. But the key to that deal is the guy standing behind him in the backfield.

Here's who stood out on Day 16 of 49ers training camp. Keep in mind, Mac Jones sprained his knee in the 49ers' preseason win over the Raiders on Saturday.

"If the 49ers want to lighten Christian McCaffrey's workload, they must add a durable running back to the rotation," Moton wrote. "Robinson can grind out yards between the tackles, which would allow McCaffrey to stay fresh for the length of the regular season."

The 49ers wisely have some key veterans, most prominently Nick Bosa, Christian McCaffrey and Trent Williams, on schedules designed to keep them fresh and out of the fray from time to time. Quarterback Brock Purdy is a leader in a more reserved, analytical way. Deommodore Lenoir is stepping up to push the secondary.

The injury list for the San Francisco 49ers went through a bit of a shuffle with a few key players returning from injuries Tuesday while significant questions remain on several others just a week before NFL rosters will be cut to 53 players.

Isaac Guerendo and Renardo Green stood out during San Francisco 49ers practice Tuesday as they returned from their respective injuries.