EDEN PRAIRIE, Minn. (AP) — Jerick McKinnon has had a lot to learn this year, more than just the speed of the NFL and the nuances of Minnesota's offense.

The rookie was never really a true running back before this season, either.

McKinnon spent much of his time at Georgia Southern as an option-style quarterback, carrying the ball for the FCS powerhouse plenty of times but not in a traditional way. He even played some cornerback and wide receiver there.

The Vikings (2-5) drafted him in the third round, with a pick acquired from Seattle in the Percy Harvin trade, with the belief that he could be a viable alternative to Adrian Peterson.

That very plan had to be put into action quickly. With Peterson on paid leave awaiting trial in Texas on a felony child abuse charge, McKinnon has passed Matt Asiata as the featured runner and topped the 100-yard rushing mark twice in the last four games.

"There's a lot different between the NFL and college. Obviously the holes are a lot smaller. You've got to anticipate better," fullback Jerome Felton said. "So his whole game has been raised the past few weeks. I've been happy for him, and hopefully he'll continue to get better."

McKinnon's elusiveness was never in question. His nickname in college was Jet, and his 40-yard dash at the NFL scouting combine — 4.41 seconds — was the second-fastest among participating running backs.

What hadn't been proven was the 5-foot-9, 210-pounder's ability to run between the tackles. So last week, before the Vikings faced what was then the league's leading defense against the run at Buffalo, coach Mike Zimmer challenged the running backs to improve their production after the first contact by an average of 3 yards. McKinnon passed the test.

This season, his average per carry after contact is 2.6 yards, according to STATS research. That's good for third in the NFL for players with 30 or more attempts, behind the New York Jets' Chris Ivory (3.0) and Chris Johnson (2.7).

"I just try to keep my legs moving, not go down easily, not be tackled after one tackle," McKinnon said. "Sometimes I came up short of that, but it's something that I'll keep working at. I feel like it's only going to get better."

McKinnon isn't just a run-around-the-end ball carrier, either. He's averaging 6.8 yards on 27 rushing attempts through the middle, according to STATS.

"Whenever the ball is in his hand, he's going to make a play. The first guy doesn't usually bring him down in the open field," quarterback Teddy Bridgewater said. "He's a guy who's very exciting to watch and very exciting to be in the backfield with. He's going to do some great things for this team."

The Vikings have said they want to give Asiata a similar number of carries, but McKinnon has made that difficult. McKinnon has 30 carries over the last two weeks, and Asiata has eight.

"Jerick has played well. I thought he did better in pass protection last week, I thought he ran the ball physically last week and he has a chance to make explosive plays, and that has nothing to do with Matt," Zimmer said.

Pass protection, in many ways, is the most important part, and an area in which rookies, especially smaller ones like McKinnon, often struggle. While he has yielded plenty of pressure from opposing rushers, he made strides against the Bills.

Perhaps the Vikings have found their permanent replacement for Peterson, rather than just a complement.

"That's not my decision, not in my control. All I can do is, when my number's called, do what I can," McKinnon said.

NOTES: Zimmer had a second procedure Tuesday for kidney stones that popped up last week. He joked as athletic trainer Eric Sugarman was addressing the team that they should show the players video of the operation. "I think there would have been some throwing up," Zimmer said. ... Center John Sullivan (concussion) was held out of practice and right guard Vlad Ducasse (knee) participated on a limited basis, with Joe Berger and Mike Harris remaining in their places. Zimmer said Sullivan and Ducasse "should be fine" to play Sunday at Tampa Bay (1-5).