"He's at the hospital right now," Houston coach Bill O'Brien said after his team's 16-13 win. "I think he's doing OK considering what happened. I think he's going to be OK, but I don't know any details yet."
Johnson sustained the concussion when he landed hard on the turf while defending a pass from Jimmy Garoppolo to Marquise Goodwin on the first series of the game. The cornerback was down on the ground while he was checked out by the training staff after he landed on the sideline. Johnson was eventually able to walk off the field under his own power and was taken to the locker room.
Texans receiver Sammie Coates also suffered a concussion in the second half and was ruled out for the game. He had three receptions for 32 yards in the win.
Johnson, a 2015 first-round pick, is expected to start alongside cornerback Johnathan Joseph this season. Johnson has dealt with injuries the past two seasons and has played in just 18 of 32 regular-season games in that span.
In 12 games in 2017-18, Johnson had 45 combined tackles and two passes defended. According to Pro Football Focus, he was ranked 121st out of 121 eligible cornerbacks last season.
Johnson was replaced by cornerback Johnson Bademosi on Saturday.