49ers RB Jordan Mason, Christian McCaffrey's replacement, has to go to the locker room with an injury

Without Christian McCaffrey, Jordan Mason was a revelation. He was one of the best running backs in the NFL.

Can the San Francisco 49ers get a similar performance from their third running back on the depth chart? Maybe they need to find out.

Mason was off to a good start Thursday night when he was tackled and immediately grabbed by his shoulder. He lay there for a while while the trainers looked after him.

Not many teams have a completely solid third running back option on the roster, although the 49ers' scheme seems to make everyone better. Rookie Isaac Guerendo is behind Mason on the depth chart. He's an athletic fourth-round pick but had just 41 career yards before Thursday. Patrick Taylor Jr. is behind Guerendo. Before Thursday, he hadn't had a carry all season. Deebo Samuel Sr. also grabs a tailback, but the 49ers wouldn't want to turn him into a permanent tailback.

The 49ers may have missed McCaffrey in some ways, but Mason had replaced most of his production. After five weeks, he was second in the NFL in rushing yards, behind only Derrick Henry. Mason had 536 yards, more than 100 yards more than any other defender except Henry.

McCaffrey missed every game this season with a calf/Achilles tendon injury. He is expected to return at some point this season. If Mason's injury is serious, getting McCaffrey back will become more urgent.