Who knows exactly when Asher Allen suffered his concussion Sunday. Yes, it was some time in the first quarter. Maybe it was on Allen's seemingly routine tackle of Saints receiver Marques Colston, a play that left the Vikings cornerback flat on his back momentarily and feeling a bit off.

But maybe that was just the thump that exacerbated the shot he had taken two plays earlier when bringing down 225-pound running back Chris Ivory.

What Vikings coach Leslie Frazier knows for sure is that when Allen stood up after tackling Colston, he didn't seem all there.

So Frazier called to Allen, trying to get him off the field. Only Allen didn't respond immediately.

"I asked him the other day, 'Could you hear me yelling your name to get off?'" Frazier said Wednesday. "He said, 'I could hear somebody yelling. But I didn't know where it was coming from -- in the stands or where.'"

This is the modern-day NFL, where head injuries might not be significantly more prevalent than they were years back. But they certainly are drawing greater attention -- from all angles.

Thanks to a mini-controversy in Cleveland, where two weeks ago quarterback Colt McCoy wasn't tested for a concussion and continued playing after absorbing a vicious helmet-to-facemask blow from Pittsburgh's James Harrison, the NFL installed yet another safety measure this week to monitor head injuries more closely.

From this point forward, a league-appointed certified trainer will be in the press box of every NFL game, in charge of monitoring head injuries while staying in close contact with both sidelines.

"Considering the collisions that happen in our game," Frazier said, "to have someone there with the background expertise to evaluate some of the potential concussions that happen, I think it is probably wise."

Head hits

In a season full of head-spinning events, the Vikings have suffered more than their share of concussions. Safety Husain Abdullah was placed on injured reserve Nov. 30, 16 days after suffering his second concussion.

John Sullivan and Jamarca Sanford each left the Vikings' Week 6 game in Chicago because of concussions and each sat out the following week.

On Wednesday both Allen and guard Steve Hutchinson missed practice due to the concussions they suffered against New Orleans.

Hutchinson's came on a routine running play when his head was driven into the turf. He was initially treated for a cut lip and returned for the Vikings' next two series. But ...

"When they began to run their tests afterwards, they realized it was more than just the pain he had in his mouth that was affecting his head," Frazier said.

That's where the NFL will try to intervene, hoping to catch concussions much quicker, leaving nothing to chance with players so often ignoring symptoms and sideline personnel so rushed and spread thin that they can't always properly diagnose head injuries.

"As players, a lot of us live in the moment and don't think about the future," Vikings defensive end Brian Robison said. "So your stubborn instinct is to say, 'I'm fine. Let's go back out there.' But later you come to find out you're not fine."

Delayed reaction

Robison suffered the type of blow to the head that seems most concerning, a wallop against Denver that was enough to leave him wobbly but not severe enough for him to know he had a concussion.

Slow-motion replays showed Robison running into a 575-pound wall, his head smashing into Denver lineman Orlando Franklin while his upper body slammed into the back of teammate E.J. Henderson.

"I thought I had just gotten knocked a little silly," Robison said. "I came up and went cross-eyed for a minute. But once the cross-eyed feeling went away, I felt fine. I remembered everything. Seemed like I was OK."

The Vikings held Robison out the rest of that game. But it wasn't until the next day when he tried running on the treadmill that he was finally convinced something wasn't right.

"I felt some head pressure and got a pretty good headache," Robison said. "I had never had a concussion before. Until you actually have one you don't realize how long it can linger."

NFL steps up

Running back Lorenzo Booker had a similar experience, banging his head during the first half of the Vikings' Week 7 game with Green Bay. Booker had an immediate headache -- which he kept to himself for the rest of the game and for two more days before finally alerting head athletic trainer Eric Sugarman.

"When I started feeling a little foggy, I finally said something," Booker said. "It just felt like it was becoming work to keep my eyes up. I felt like I wanted to just put my head down and do nothing."

Booker's hesitance to speak up infuriated the ultra-cautious Sugarman.

"In my mind, I get headaches a lot," Booker said. "So if I come and tell [the staff] my head hurts every time my head hurts, I'm going to be in the training room all the time."

The back-up running back missed the Vikings' next game in Carolina and continued his recovery with Sugarman being extra persistent in obtaining honest feedback.

Six weeks later, with a big-picture perspective, Booker knows players can't live with a sense of invincibility and is happy the NFL is stepping in with heightened concern.

"It's scary," Booker said. "I'm trying to be here, man. This is not something you want to mess with. I'm all for extra precautions."