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The Vikings hope that, in his third NFL season, running back Dalvin Cook will finally reach his full potential. Given his injury history, they need to have other plans. And with Latavius Murray gone, the No. 2 spot on the depth chart becomes critical.

For now, rookie running back Alexander Mattison holds that job. Reading between the lines (and, based on the video, watching between the pauses) of coach Mike Zimmer’s most recent press conference, it appears that Mattison has work to do in order to be trusted as the second-string tailback.

“I’ll try to say this the correct way,” coach Mike Zimmer said Sunday when addressing his tailbacks, as the typically-blunt Zimmer searched for the right words. “I think Mattison has got a really bright future. I think the other two guys [Ameer Abdullah and Mike Boone] can help in change-of-pace situations. Mattison is going to have to continually work on his pass protection.”

In other words, running the ball is only part of the job. Protecting Kirk Cousins from getting blown up is a big part of it, too.

“[T]he other two guys are smaller guys,” Zimmer said, in reference to Abdullah and Boone. “If they’re going to be in there on third downs, they’re going to have to block bigger guys, so that’s going to be their deal as well. That part of it, I think we feel like they all can run, they’re all smart enough to run the offense and things like that. But it will come down to third downs and those areas.”

So the second-string and/or third-down tailback will win the job based on whether he can indeed be trusted to help pick up blitzers in passing situations. For Mattison, who had 30 yards rushing and caught a short touchdown pass in his NFL debut, to fulfill his “really bright future,” he’ll need to keep working on that.