Niners RB Jordan Mason, NFL's leading rusher, questionable to ...

Jordan Mason's been a sensational replacement for the injured Christian McCaffrey.

Now, the San Francisco 49ers might need a replacement for Mason, who suffered a shoulder injury in the second quarter Thursday night against the Seahawks.

Mason walked to the locker room for X-rays and was deemed questionable to return, which he did for one play in the third quarter. However, he went to the sideline immediately after an 8-yard run. He later made his way to the blue tent. Before and after his time in the tent, Mason could be seen working out his injured left shoulder.

Mason had rushed for 73 yards on nine carries, increasing his NFL-leading season rushing total to 609 yards.

In Mason's absence, rookie Isaac Guerendo and Patrick Taylor, along with wide receiver Deebo Samuel, have been filling in at running back.

Just how serious Mason's ailment is for this game and beyond remains to be seen.