Rookie David Johnson has been largely impressive through two games, even in limited playing time.

In Week 1, he turned his lone reception into a 55-yard score; in Week 2, he returned the opening kickoff 108 yards for a touchdown and also totaled 42 rushing yards plus another score.

Despite his efficient production, head coach Bruce Arians isn't ready to just give Johnson more playing time, pointing out one key part of his game that may need work.

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"They don't play fast enough, especially in the passing game," Arians said, via the team website. "We haven't seen him pass protect. He missed all of that stuff in training camp. He's big enough and everything, but until he takes one and gets a little bit better at it … you can only do so much (with him in there) if you can't pass the ball."

Johnson has clearly made his imprint early on and impacted both games for the Cardinals.

He's earned enough playing time, but the coaching staff has yet to decide how much playing time the rookie will see going forward.

"(David) will have a vital role every week," Arians said, via the team website. "Just how big, we will wait and see."