Just as Bengals running back Joe Mixon was beginning to get comfortable with the NFL game, the team has officially ruled him out for rest the team’s Monday night game vs. the Steelers with a concussion.

The rookie running back took a big hit from both sides and was down on the ground for awhile until he was able to walk off under his own power to go through testing on the sideline.

Mixon, 21, had started off his NFL career fairly slowly given his lofty status coming out of the draft. Many experts speculated that the former Oklahoma Sooner was just as, if not more talented than top backs like Leonard Fournette, Christian McCaffrey and Dalvin Cook.