MINNEAPOLIS -- Perhaps the biggest question surrounding the Minnesota Vikings' defense heading into 2017 is whether Mackensie Alexander can shake off a disappointing rookie season and prove he's a worthy successor to Captain Munnerlyn at the nickel cornerback spot. And given how many of Alexander's struggles were in plain sight last season, it's worth spending some time on what coach Mike Zimmer had to say about the second-year corner last week.

"It looks like he’s grown up quite a bit," Zimmer said in a conference call with reporters on Friday. "He’s matured a lot. We’ve had him in there at the nickel position and he’s done a really good job. He’s been impressive these first three days. Very few mental mistakes and he’s a really good athlete. He’s got great acceleration and when he goes out to corner he does a nice job as well. But, for right now he’s focusing really hard on the nickel position."

Vikings coach Mike Zimmer said that he has seen improvement in Mackensie Alexander's coverage skills this offseason. "When he's had to cover guys one-on-one, he's done a good job," Zimmer said. Stacy Revere/Getty Images

Maturity, for Alexander, was the big question coming into the 2017 season. Zimmer said as much at the NFL owners meetings, when he was asked about the Clemson product's progress. "He's kind of -- what's the best way to say this?" Zimmer said. "He's kind of a guy that has a ton of talent. I think he's a good kid. He just needs to be more consistent with really everything: practice habits, things like that. A lot of times, young guys coming in -- I’m not saying him particularly -- they come in and they don’t trust enough, they’re not trusting enough [of coaches]. It’s just that kind of stuff.’’

Young corners are given a wealth of resources in Minnesota, between Zimmer, defensive backs coach (and four-time Pro Bowler) Jerry Gray and Terence Newman, and it behooves players like Alexander to tap into those resources. Last week, Zimmer didn't hold back much when talking about how significantly the corner has changed.

"I know that he probably thought he should’ve been playing more [in 2016]. But, I don’t think he really knew to go about doing things the right way," Zimmer said. "This is how much the kid’s grown up; so, he actually spoke to our rookies the other day. He talked to them about how he’s grown from last year with some of his attitude things and what he could’ve done better. Hopefully some of these rookies were listening."

Given how much nickel corners play in the NFL -- and how much quarterbacks like Drew Brees and Ben Roethlisberger figure to go after Alexander in the first weeks of the season -- it's incumbent upon Alexander to quickly show the Vikings they can count on him. His approach in the Vikings' offseason program would seem to suggest he's gotten the message.

"I’ve been impressed," Zimmer said. "He’s done a nice job in run support and he’s done a good job in coverage areas. When he’s had to cover guys one-on-one, he’s done a good job. So, if he’ll continue to keep the same attitude, mindset that he has, I think it’s all systems go for him."