Practice had been over for a while Thursday, but Vikings receiver Jaymar Johnson was still on the field.

He and assistant coach Jimmie Johnson were playing catch, with Jaymar Johnson wearing a fancy-looking pair of shades. Fancy and special. Those glasses, obtained from the trainers, flicker quickly between full vision and a black screen, designed to induce maximum concentration from anyone hoping to catch a football.

"It's unbelievable how it can focus you," Johnson said.

Johnson, itching to play after a year on injured reserve, hopes to catch a lot of footballs, and he is willing to do anything to get an edge.

He is not alone.

The Vikings are likely to keep five wide receivers. Three appear to be locks: Bernard Berrian, Percy Harvin and Michael Jenkins. Reliable veteran Greg Camarillo would appear to be safe but is probably not a lock. Then you have Johnson, Devin Aromashodu, Juaquin Iglesias and Emmanuel Arceneaux fighting for what could be one or two spots.

And that only makes Saturday's game in Seattle that much more important at one of the most hotly contested positions on the roster. Harvin (bruised ribs) and Camarillo (groin) will miss the game, providing a good opportunity for the others.

"That's one of the reasons we didn't want to rush Percy or Greg," Vikings coach Leslie Frazier said. "We really need to evaluate that position and when we talked about it, we said, 'Hey, you know what? We know Camarillo, we know Percy. We need to get to know these other guys much better so we can make the right decision.'"

The player who makes it might not be the best pure receiver, according to wide receivers coach George Stewart.

"I'm a former special teams coach in this league -- I did it for 11 years -- and that's always been paramount," Stewart said. "Sometimes you may keep the better special teams player than the better receiver because he can help you for 20, 22 snaps a game on special teams."

All the competitors for backup spots bring something to special teams. Johnson is competing hard for the job of returning punts. The others are playing on kick and punt teams; Aromashodu flashed some good signs on coverage teams in the preseason opener, enough to draw raves from special teams coordinator Mike Priefer, according to Stewart.

"I'm trying to do just what they brought me in to do, and that's to catch the ball and be an asset on special teams," Aromashodu said.

Aromashodu caught a career-high 24 passes with four TDs for Chicago in 2009, including the overtime winner against the Vikings on Dec. 28. But he did not flourish under new Bears offensive coordinator Mike Martz, dropping to 10 catches last season. Arceneaux was signed as a free agent after two productive seasons for the BC Lions in the Canadian Football League. Iglesias is also from Chicago, having spent most of last season on the Bears' practice squad before being signed by the Vikings before the regular-season finale.

Johnson is mainly an outside receiver, but his punt returning could help his chances. The others have positional flexibility, able to line up outside or in the slot. Johnson broke his thumb in preseason last season and spent the year on injured reserve. The sixth-round pick by the Vikings in 2008 saw his only action in 2009 and returned 16 punts that year.

"With me missing out on last year, I treat every game like it's my last one," Johnson said of Saturday's opportunity. "I appreciate each one."