The 37-year-old veteran has not played for the Flyers since November, and has gone through a long and difficult battle with post-concussion symptoms.
It would be remarkable if Pronger was able to make a return to the NHL, but even if he has played his last game, there's no question that he's Hall of Fame worthy.
Pronger won the Hart and Norris Trophies in 2000 as a member of the St. Louis Blues, becoming the first player to win both awards in the same season since Boston Bruins legend Bobby Orr in 1972 (which was the last time a defenseman won the Hart Trophy).
If Nicklas Lidstrom didn't win six Norris Trophies in the 2000s, Pronger would likely have won a few more of those as well.
Pronger's ability to completely transform teams is simply amazing. Just the addition of him alone is enough to turn an average team into a legitimate contender in the playoffs. Surprisingly, he has been traded four times in his career, but each place he went immediately got better defensively when he arrived.
When he was traded from the St. Louis Blues to the Edmonton Oilers, Pronger led the Alberta club to the 2006 Stanley Cup Final against the Carolina Hurricanes. The Oilers eventually lost the series in seven games, but it was still a great accomplishment since Edmonton was a No. 8 seed. Pronger's play at both ends of the ice was the major reason why the Oilers came one win away from another championship.
He was then traded to the Anaheim Ducks in the 2006-07 season. Pronger and future Hall of Fame defenseman Scott Niedermayer helped the Ducks win their first ever Stanley Cup that year in a five-game series victory over the Ottawa Senators. That season, Pronger set a career high with 59 points.
At 6'6" and over 200 pounds, very few defensemen in the history of the NHL have been able to affect games like Pronger. He's a guy nobody likes to play against, which is one of the biggest compliments you can give a hockey player. Pronger gets under his opponents' skin, and sometimes he does go too far, but it's all part of the imposing style of play that makes him so effective.
His tremendous size and toughness made him a nightmare for the league's top forwards, and one of the most intimidating forces we have seen in quite some time. You can put Pronger on the ice, and not have to worry about a mismatch. His size makes him a unique player, just like Zdeno Chara of the Boston Bruins.
Pronger isn't only a defensive force. He has been an excellent offensive player throughout his career, racking up 698 points (157 goals, 541 assists) in 1,167 games. He is able to run a power play and lead the penalty kill, and is one of the most complete defensemen hockey fans have seen in some time.
Sure, Pronger hasn't been the most likable player of his generation. He didn't leave Edmonton well, and many Oilers fans are still angry that he didn't play for the team beyond the 2005-06 season despite being under contract.
However, you cannot dispute the fact that Pronger is one of the best defenseman of the last 25 years. Is he one of the 10 best of all time? No, but he is certainly in the top 15 or top 20. Not only is he a great player, he's a fantastic leader too.
Pronger shouldn't feel bad about not being able to return to the NHL if his health prevents him. He made an impact on the ice that few defensemen have ever been able to make, and will be remembered as one of the best d-men ever.
Nicholas Goss is an NHL lead writer at Bleacher Report. He was also the organization's on-site reporter for the 2011 Stanley Cup Final in Boston. Follow him on Twitter.