Kell Brook's stunning defeat at the hands of Errol Spence, Jr. could be a costly one for the 36-2 boxing great and framer IBF World Welterweight champion. 

Brook took a knee in the 11th round, electing to stop the beating he was suffering to Spence. It was the second loss in a row for Brook, who had won 36 fights in a row prior. The 31-year-old boxer was having trouble with his vision and knew he had to protect himself. 

Brook suffered a broken left eye socket during the bout, the same injury he sustained when he lost to Gennady Golovkin last September. A titanium plate was implanted into his face to repair the damage, but once again it was a problem for Brook. 

The injury is serious enough that it's forcing him to undergo surgery to repair it again, reports Nick Parkinson of ESPN, which leaves serious doubts about him fighting again in 2017. Many are even wondering if Brook can or should fight again after a disappointing showing with dangerous results.

"I'm devastated. I knew from round seven that the eye had gone and progressively as the rounds went on. I tried to get through the fight and it kept going double-vision and then coming back into line," Brook told Sky Sports.

"In the later rounds 10 and 11, especially 11th round, it stuck there and that's why I went down on one knee and I remember the surgeon saying to me after the Golovkin fight if you would have gone another round or so you could be blind so I've got that going through my mind as well."

That's a scary story, and it appears Brook may have dodged permanent damage to his vision twice. Taking a knee is uncommon in boxing, especially from major stars, but it was the right move considering what doctors told him in the past.

Kell was clearly losing the fight, and barring a surprising knockout blow to save him, the judge's were likely sending the victory to Brook. Deciding to play it safe was the right move for Brook, and that's what has led many to wonder if retirement might also be the right move.

Brook has stated that he doesn't plan on retiring, and that he doesn't want to go out on a losing note. Even in ESPN's injury report, Parkinson mentions that Brook's career is "in the balance" with his history of eye injuries being severe enough to force him into retirement. 

Every competitor wants to come back, but not every one has a good enough head on their shoulders to know when it's time to take a knee. Brook will have to seriously consider taking one more knee depending on how his latest injury recovers.