An injury, depending on the severity, can have a damaging effect on the player who suffers it and the team that has to deal with it.
A string of physical ailments can stunt a potential star's growth or weaken a career that could have been stronger if they player had been healthier.
Presented now are the delicate group of 10 that dazzled on the field...but just couldn't always stay on the field.
During his long tenure with the Eagles, McNabb was battered verbally by Philadelphia fans as well as battered by opposing defenses.
McNabb's first major injury also coincided with one of his best performances. Against the Cardinals in 2002, the Eagle QB suffered a broken ankle while being sacked in the first quarter. Playing through the pain, he threw for four touchdowns in a victory.
He went through a sports hernia and a sore thumb in 2005, an ACL tear in 2006 and a broken rib in 2009.
When his career in Philly was finished, McNabb had led the Eagles to five NFC Championship Games and a Super Bowl, all while setting multiple team records.
He was a regular winner of the Comeback Player of the Year thanks to a penchant for being bitten by the injury bug.
Pennington emerged as the starting signal caller for the New York Jets by leading his team to an AFC East title in 2002. The next season, however, didn't go as smoothly.
He suffered a fracture on his non-throwing hand in the final preseason game of 2003. Pennington missed the first six weeks of the regular season.
A torn rotator cuff in 2004 forced him out for three contests following a strong start. That injury would haunt the former Marshall QB into the next year.
It's no surprise that his body failing him caused him to stay out of football in 2011.
When this safety played, he made a significant role in the defense.
The trouble was, it was hard for him to play for a significant stretch of time.
Fortunately for the Indianapolis Colts, Sanders was healthy for the run to a Lombardi Trophy in Super Bowl XLI.
Unfortunately, he participated in more than six games in a season only twice (2005 and 2007).
Sanders now is a member of the San Diego Chargers. Surprise, surprise...he was placed on the injured reserve list on Sept. 28, 2011.
Throughout his Jets career, Joe Namath led the league in coolness and knee operations.
His arm was strong, but his legs were brittle.
Between 1970 and 1973, Namath played in just 28 of New York's 58 games. When he did participate, he showed flashes of his old self.
The aches and pains didn't prevent Namath from being the MVP of Super Bowl III, reaching the Hall of Fame and becoming one of the most important figures in pro football history.
The most electrifying quarterback in the game today has also had his share of trips to the disabled list.
With his penchant for running the football and his small frame, it's not really a shocker that Michael Vick has been prone to injuries.
On the scale of significance, the worst came when he suffered a fractured fibula in a 2003 preseason contest. He would be out for the first 11 games of the year.
Being a member of the Eagles hasn't made him any healthier. While Vick has certainly improved as a passer, he was rocked with rib injuries in both 2010 and 2011.
With every step he took on the field, it could have been his last of the game.
That's how fragile Todd Heap is. If you made him the starting tight end on your fantasy team, it was wise to make sure to have a backup.
The Arizona State product missed chunks of 2004, 2007, 2009 and 2010. During the time he has been active, Heap has accumulated more than 5,700 yards and has scored 41 times.
His original team, the Baltimore Ravens, released him following the 2010 campaign. He latched on to the hometown Arizona Cardinals for 2011.
Most of the players on this list qualified due to injuries they suffered on the football field.
The Carolina Panthers' Steve Smith is an exception.
He broke his left forearm in June 2010 while playing flag football, just six months after suffering the same fracture in a regular season game. That was the latest in a long line of bumps and bruises for the three-time All-Pro.
Smith missed all of 2004 with a knee injury and recovered to have a spectacular 2005.
Now that he has Cam Newton, the Panthers hope he stays healthy for the foreseeable future.
As his son has just made a name for himself at the University of Wisconsin, Al Toon did the same for the Badgers back in the 1980s.
From there, Al went on to play his entire pro career with the New York Jets. It would be a career that had 517 receptions, 6,605 yards and 31 touchdowns. But it was also a career that was cut short due to the accumulation of nine concussions.
He would retire at just 29 years old.
Had it not been for a broken foot, Schaub would have guided the Houston Texans to their first playoff appearance. Nevertheless, he was partially responsible for putting them in position to reach the postseason.
Schaub's hopes for successful campaigns were cut short in his first two years with Houston. In 2007, he was able to fight through injuries and missed games to get the club to .500. In 2008, a knee injury forced backup Sage Rosenfels to come in for four weeks.
The USC stud won the Heisman in 2005 with his immense talents. That was taken away a few years later.
As it turns out, many games on the pro level have seen him missing in action as well.
Bush's speed was slowed with microfracture surgery in January 2009 following a series of injuries.
After winning a Super Bowl with New Orleans the next year with multiple ailments, he would get 2010 off to a bad start. A broken bone in his right leg, suffered in Week 2, made him sit out for a month and a half.