What do Santonio Holmes, Darrelle Revis, and Brian Orakpo have in common? They’re all missing in action until next year thanks to serious injuries. Each year a group of players have the unfortunate experience of missing significant time due to injury, and also risk losing their position and playing time for the same reason.

Detroit’s running back Jahvid Best awaits tests this week to determine if he’ll finish the season on injured reserve after two concussions last year, and he hasn’t played a down in 2012. So far Adrian Peterson is returning to strong form after missing most of last season to knee surgery. When you’ve suffered a devastating injury and miss an extended period of time, every minute you’re injured is another minute someone else is filling in your position. Don’t kid yourself, professional athletes worry about losing their jobs to injury more than they’ll ever reveal.

Ask Drew Bledsoe about when he opened the 2001 season as the New England Patriots starting quarterback before Tom Brady finished off the year as the youngest quarterback ever to win the Super Bowl, and the Super Bowl MVP. Some guys can play through smaller injuries thanks to incredible pain thresholds, but serious injuries don’t leave you with a choice even though they raise plenty of questions among coaching staffs. Will he fully recover? Did he lose a step? Is that player worth the health and financial risk? I wonder who else is available? Who gets his playing time?

Ask Peyton Manning how he became a Bronco.

I’ve experienced the sting of a season-ending injury myself, and know the frustration it carries.

My second year of college ended in training camp after sustaining a bulging disc in my lower back. The injury occurred at practice in half strip during a routine run and catch. If you’ve never endured sciatic pain, think of intense shocks of electricity running from your lower spine down the back of your legs.

Two days before our season opener it was decided I would take a medical redshirt, meaning I would sit out the entire year without sacrificing a year of eligibility. What followed was the longest offseason of my life. In fact I went through two off-seasons between games in uniform.

After the injury and a three-month layoff from any physical activity including jogging, running, and weight lifting, I started a scheduled battery of physiotherapy, chiro, and core rehab, or as I called them: not playing, not playing, and not playing.  I wasn’t a starter yet when I was injured, but going from second-string to redshirt means you spend game days on the sidelines in a tracksuit for moral support. See you next year.

Broken bones heal the fastest thanks to steel plates and screws. A dislocation of anything is bad. Head injuries and torn ligaments are pretty terrible, and anything involving surgery is a worst case scenario.

The risk of setbacks and re-injury are present daily during the recovery process. I have seen careers end in the worst way possible, and I still consider myself lucky. The unpredictable nature of injuries comes from the fact one can happen during a collision on the field or a slight mishap off of it.

The year after I hurt my lower back, one of our starting cornerbacks suffered a concussion in the second game of the year while returning a punt, and he missed the rest of his junior season. His second concussion came early in his senior season while making a game-saving tackle. After taking a medical redshirt, he focused on rehab and recovery. Two months before the start of fall camp the next year, he fainted on a treadmill during supervised physio and struck his head on the way down, collecting his third and instant career-ending concussion. For a promising player and team leader, it was a devastating blow.

In professional football players are well aware they can lose their spot to another player, an injury, or a combination of the two at any time. Maybe it will be the hungry backup who steps in for a few weeks and lights up the field while you’re out with an sprained ankle. Or it could be that rookie from this year’s draft, tagged as an understudy. The team could always opt to upgrade in free agency, just to add depth to the roster “in case something happens.” Or a new coach could take over and bring his own man.

The uncertainty is why the fiercest competitions happen in practice. There aren’t enough positions on the field for everyone on the roster, and therefore you have to earn the right to battle other teams. In pro football, the difference between starters and the practice roster is several income brackets and a guaranteed contract.

The nature of the next man up philosophy in football means the team keeps rolling full steam ahead with whatever parts are available. Feelings are put aside, and the myth about not losing your position due to an injury might be true only for all-stars at the peaks of their careers. Almost everyone falls off at some point, and no job is as safe as players like to believe.

Not everyone is lucky enough to catch up to the machine once they get back in the running. The best thing to do is never get injured. Good luck with that.

Luke Purm is a freelance writer and former college football player (a wide receiver at Simon Fraser University) with an inside look at the sights and sounds from the huddle, down the field, through the air, in the endzone, under the pile, out of the locker room, on the scoreboard, and everywhere else football sweats, smells, yells, breathes and collides with life. Follow him on Twitter.