There are questions as to how productive Johnson can be after a less than stellar 2019 season in Arizona.
Johnson had a breakout season in 2016, missed most of the 2017 season with a wrist injury, before returning in 2018 to a decent production level (258 carries for 940 yards, seven touchdowns; 50 catches for 446 yards, three touchdowns).
Johnson was held back by an ankle injury and was eventually replaced by Kenyan Drake, who the Cardinals acquired in a midseason trade from Miami.
The change of scenery and how the Texans utilize Johnson could benefit the five-year pro.
O'Brien certainly believes so.
"I think when you look at David Johnson, he's a three-down back who's had some productive years," O'Brien said, adding how he likes Johnson's fit into the Texans' offense. "Plus, the type of guy he is, just being on the phone with him a few times, having met him face-to-face when he was coming out in the draft. I'm just so excited about having him."
O'Brien, seemingly in defense of his moves as general manager this offseason, emphasized that he believed the key to having the best team is having a room full of productive players.
It appears O'Brien sees the value in having the likes of Johnson and wide receivers Brandin Cooks and Randall Cobb -- all acquired via trade or free agency since March -- versus any one star player.
"The key to having the best team is not just having the best player," O'Brien said. "We have a lot of really good players. We've got players that are Pro Bowl players. We've got players that are tremendous role players. But really the key to having the best team is to have a room full of productive players -- layers and layers of productive players relative to what their roles are on the football team.
"I'd say contracts, injuries and the salary cap are a part of the game as we know it. And those have to come into play in every decision we make relative to the personnel on our team."
Johnson, who is expected to be the Texans' No. 1 running back, meets with the media Friday morning.
Johnson and Hopkins both passed their respective physicals in recent days.
The Texans could still add another back with the No. 40 overall pick.
They have reportedly shown interest in Ohio State prospect J.K. Dobbins, though O'Brien also spoke of the Texans' needs on the defensive side of the ball.
The Texans could use some help on the defensive line and add depth to the secondary.