Deion Sanders isn't walking through that door. Neither is Bo Jackson. In the late 1980s and early 1990s, both Sanders and Jackson excelled in two professional sports, the MLB and the NFL.
Today, that is nearly unheard of. With the amount of training that goes into every offseason and the amount of money that owner have invested in their players, a multi-sport star is impossible to imagine in 2011.
That's not to say that there aren't guys out there who are athletic enough to do it. Alex Rodriguez and LeBron James are two of the most athletic people on the planet, and it's not inconceivable to imagine them playing another sport.
In no particular order, here are 10 athletes who could excel in a sport other than their own.
Julius Peppers is one of the most athletically gifted players in all of football. At 6'7", 283 lbs, Peppers possesses a unique blend of size and speed that makes him nearly impossible to block on the football field.
That quality could also translate into success on the basketball court.
Peppers played basketball at UNC for two years as a walk-on and was an integral part of the Tar Heels' 1999-2000 team that made it all the way to the Final Four.
With his experience and size, Peppers could conceivably make an impact in the NBA today.
As we are all quite aware, LeBron is one of the most physically gifted athletes in the history of professional athletics. He's as fast as Allen Iverson and as strong as Karl Malone, with the passing acumen of a young Magic Johnson.
The combination of skills he possesses is practically otherworldly, and the basketball court isn't the only place he's dominated.
LeBron was an All-State receiver in high school, and it's widely accepted that he could contribute in the NFL as a tight end.
With his leaping ability and huge hands, he could be unstoppable in the red zone.
As a student at Westminster Christian High School, A-Rod excelled on the gridiron as well as the diamond.
He was recruited to player quarterback at Miami (FL) and was intent on going there before being drafted by the Seattle Mariners with the first pick in the 1994 MLB Draft.
At 6'3", 228 lbs, Rodriguez has prototypical size for an NFL QB, and his arm strength becomes apparent every time he fires a frozen rope across the field to Mark Teixeira.
Tony Romo is a good quarterback, and not a bad golfer. In 2004 he tried out for the EDS Byron Nelson Championship and in 2005, he attempted to qualify for the U.S. Open.
While he failed to qualify for either event, the fact that he even tried out speaks volumes about his game.
If he were to dedicate his athletic life to improving his game, their is no doubt that Tony Romo could compete at the PGA Tour level.
As it stands, being a starting quarterback for one of the highest profile teams in the NFL takes up most of his energy, leaving little time for him to improve his golf game.
At 6'9", 345 lbs, Jonathan Ogden had the size and quick feet to be one of the best left tackles ever to play the game.
Shaquille O'Neal, when he was a younger man, had some of the quickest feet and best hands for a big man in all of basketball.
At 7'1", 325 lbs, Shaq could easily protect the blind side of any NFL quarterback.
Since his real weight is probably closer to 350 pounds, Shaq possesses great size for a left tackle. If he would have played in the NFL, there's a chance that we would have been looking at Shaq as one of the best OT's ever to play the game.
At Jefferson Davis High School in Houston, Texas, Carl Crawford was heavily recruited as an option quarterback. Schools like Tulsa, Oklahoma, USC and Florida all offered him a scholarship.
He settled on going to Nebraska, but elected to forgo his college football career after he was drafted by the Tampa Bay Devil Rays in the second round of the 1999 MLB Draft.
He doesn't possess prototypical NFL QB size, but at 6'2", 215 lbs, Crawford has the speed and quickness to be a big, physical corner or nickel back in the NFL.
Crawford is almost the exact same size as Antonio Cromartie, and is probably just as fast. If not for baseball, we may be talking about Carl Crawford as one of the premier corners in the NFL.
Terrell Owens, despite all his faults, is one of the best receivers ever to play the game. With 153 receiving touchdowns to his name, there is no question that T.O. dominated like few before him.
On the football field, Owens often displayed his great leaping ability, especially when he was dunking the ball through the goal posts during one of his patented touchdown celebrations.
He even proved himself to be a dominant force on the basketball court, albeit in a celebrity game. Nonetheless, it's clear that Owens has basketball talent.
Perhaps if he had dedicated himself to basketball rather than football, Owens could have been an impact player in the NBA.
Steve Nash's creative distribution of the ball on the basketball court has been well documented; it's also a talent that could serve him well on the football pitch.
Nash grew up playing soccer and played it long before he had ever even seen a basketball. His quickness and agility on the court could have served him well as a soccer player.
In the 2005 Slam Dunk Contest, Nash headed a perfect alley-oop pass to Amar'e Stoudemire, who threw it down with a 360 dunk.
Luckily for us, Nash chose to play basketball; he is one of the most entertaining and exciting players in the NBA today.
Joe Mauer was offered a scholarship to play quarterback at Florida State University, before ultimately turning down that offer when he was drafted first overall in the 2001 MLB Draft.
In his senior year of high school, Mauer threw for 3,022 yards with 41 touchdowns and only five interceptions. He was also an accomplished basketball player.
Mauer is the unquestioned leader of his team, the Minnesota Twins, and that leadership would serve him well on the football field.
At 6'5", 230 lbs, Mauer has Peyton Manning size, not to mention a cannon arm that he puts on display when gunning down runners at second base.
Chris Johnson, half back for the Tennessee Titans, recorded the fastest 40 yard dash time in the electronically timed history of the NFL Combine.
Johnson ran a 4.24 at the 2008 NFL Combine, solidifying him as a first round draft pick.
In 2004, at the Florida 4A State Championships, Johnson finished second to 2008 Olympic Bronze Medalist Walter Dix in the 100m dash.
His personal best in the 100m is 10.32, a world class time that is less than a second behind the world record.
Were he to trim his body down and train to be a sprinter, Johnson could compete at a very high level.
Mike Osterberg is a student at Penn State University and Featured Columnist for the New York Giants. Follow him on twitter @Mike_Osterberg.