Marcus Sherels' days in a Vikings uniform appeared numbered at the start of training camp, at least from an outside perception.

The diminutive cornerback realistically had little chance to make the final 53-man roster, right? Not with the secondary overhaul that took place this offseason. The Vikings needed to detonate the whole operation after what transpired last season.

Antoine Winfield (injury) and Chris Cook (legal) returned to the lineup as starters. The team drafted Josh Robinson in the third round and signed veteran free agents Chris Carr and Zack Bowman. Brandon Burton, a fifth-round pick in 2011, figured to get a closer look.

NFL coaches always preach that backups and bubble guys shouldn't count numbers in front of them, but the cornerback position looked pretty much filled as the Vikings arrived in Mankato.

So what did Sherels think when he saw all the turnover and new faces at his position?

"The same thing I thought the first day I came here: Just come in and work hard and do my best and see what happens," he said.

That simple, understated approach has served him well. As unlikely as it seemed a month ago, Sherels earned a spot on the active roster and will open the season as the team's primary punt returner. He also could see action at kick returner to limit Percy Harvin's exposure to violent collisions, especially early in the season with wide receiver Jerome Simpson serving a three-game suspension.

Sherels is recovering from an ankle sprain that kept him out of practice Monday. His availability for the opener Sunday against Jacksonville remains unknown, but the fact that he's still around serves as a testament to his perseverance.

"You've got to credit his tenacity," coach Leslie Frazier said. "He's one of those guys who's a little bit undersized, but he plays a lot bigger than he is. And he's a multipurpose guy. He does a good job for us on special teams."

Sherels survived the final wave of cuts as the team jettisoned Carr and then Bowman after trading for A.J. Jefferson. In a perfect world, the Vikings won't need Sherels to play many snaps at cornerback. He's not a frontline NFL cornerback, but the Vikings coaching staff clearly trusts him as a returner, particularly in terms of his ability to catch the ball cleanly and not turn it over.

"I take pride in trying to catch it every time," he said.

Sherels is an unlikely success story, a guy who treats every NFL workday as if it could be his last. He will always be a fringe player, forever on the bubble, his job status never secure enough for him to feel comfortable. He understands that reality but doesn't let it drag him down.

He wasn't supposed to make it this far. The former Gopher from Rochester went undrafted and started at the lowest rung possible, on a tryout basis. He weighed 162 pounds at the time and had plans to enter law school if things didn't work out. He turned that tryout into a training camp invite, then practice squad and finally a full-time spot on the 53-man roster last season.

"You never know," he said.

That's Sherels in a nutshell. It takes a crowbar to get him to open up and say more than two sentences about himself. He just quietly goes about his business. He's also unassuming physically at 5-10, 175 pounds. But he competes like he belongs in this profession, and he compensates for any physical limitations by doing whatever necessary to stick around a while longer.

"He really knows how to play football," veteran Antoine Winfield said. "He's a small guy but very smart. His acceleration is unreal. Just watch him. He's quick."

Sherels started three games last season as injuries piled up and even sacked Green Bay Packers quarterback Aaron Rodgers, although that highlight also inspires a muffled reaction from him.

"I didn't even know it was a sack until after the game," he said. "He broke the pocket and I ran up and tackled him."

Sherels doesn't know if he'll get that kind of opportunity again this season. The Vikings prefer he makes his mark on special teams, but, as last season proved, injuries could thrust him into a more prominent role. Few people would have predicted that scenario a month ago.

Sherels didn't count numbers though. He just quietly did his work and hoped that was good enough.

"I'm happy the Vikings gave me a chance," he said. "I want to prove that I deserve to be here."

Chip Scoggins ascoggins@startribune.com