The San Francisco 49ers lost the league’s leading rusher about a quarter and a half into Thursday night’s game against the Seattle Seahawks. Running back Jordan Mason left the game early with a shoulder injury.

Mason returned to start the second half, where he carried the ball from scrimmage on the first play. But he ran off the field and wouldn’t return. The sideline cameras panned to Mason several times, where he tried unsuccessfully to free his shoulder.

49ers head coach Kyle Shanahan said Mason “went back in there and it just hurt him too much.” Shanahan added that Mason thought he would be fine and could have even played in the second half if there had been an emergency.

The 49ers will know more about Mason’s injury sometime this afternoon as x-rays will be taken on Friday. Shanahan clarified that just because Mason believed he could get back in doesn’t mean his injury was minor: “Adrenaline during these games is a little different.”

Mason was well on his way to 100 yards and could possibly have surpassed his season high from Week 1 had he played a full game. Mason finished with 73 yards on nine carries, including a gain of 38 yards. Isaac Guerendo’s 76-yard run near the end of the game will make some think anyone can do what Mason did, but that’s simply not true.

If Mason is forced to miss, it would be a major blow to an offense that hasn’t started yet.

Sports Illustrated’s Albert Breer had an update on Christian McCaffrey and whether his timeline has changed:

“Back in August, when he started feeling like himself again, they stepped him up heading into the opener against the Jets. Finally the Achilles flared up on him. After the opener, they finally shut it down.

Last week he started feeling like himself again, so they started boosting him over the last few days. The good news is that there has been no flare-up. There have been no setbacks. He’s feeling good, so the Niners are optimistic about where he is. But this is a scary deal for him. He is determined to play this year. I would say the two or three weeks are crucial.

Breer said first-round rookie wide receiver Ricky Pearsall was close to being done this week, but the 49ers decided to play it safe. Kyle Shanahan said the team decided not to open Pearsall’s window because the team would not be practicing leading up to this week.