"This injury was a negative thing in the beginning but it became a positive thing at the end," said the UFC welterweight champion.
"Because it allowed me to correct my training and make it better and improve it."
St-Pierre (22-2) will test his knee and new training regimen — part of which involved training with track sprinters in his hometown of Montreal — on Nov. 17 against Carlos (Natural Born Killer) Condit who won the UFC's interim title during St-Pierre's absence.
The two 170-pound division belts will become one at the Bell Centre where the real welterweight champion will be confirmed at UFC 154 in St-Pierre's first fight since an April 2011 win over Jake Shields at Toronto's Rogers Centre.
It's a welcome return for the UFC which counts the 31-year-old St-Pierre as its biggest pay-per-view draw. GSP is literally money in the UFC bank.
St-Pierre has long been known for gruelling workouts and for taking little time off from the gym. He now believes his injury was perhaps caused by that pedal-to-the-metal training approach.
"I had the mentality that more is better, but I realize that's wrong. Smarter is always better."
As a result, he says he is enjoying his training more.
"I have more fun doing it," he said. "I'm more fired up to go train now."
That's bad news for opponents since St-Pierre's fights have always gone the way of his training. A good camp and he prospers in the cage.
The one exception was his first title defence against Matt (The Terror) Serra. St-Pierre, dogged by his father's poor health and perhaps not handling his newfound fame, was stopped in the first round at UFC 69 in Houston in April 2007.
St-Pierre often says he doesn't make the same mistake twice.
After the Serra loss, he rejigged his coaching and management support team. He hasn't lost since, winning nine in a row.
St-Pierre will need to be at the top of his game against Condit, a former WEC champion who has disposed of Jake Ellenberger, Canadian Rory MacDonald, Dan Hardy, Dong Hyun Kim and Nick Diaz since losing a split decision in his UFC debut to Martin Kampmann in April 2009.
The 28-year-old Condit is a smart well-rounded fighter who seems to be putting his game together nicely.
He is durable, as MacDonald learned after dominated the early going of their fight only to fall under a late Condit barrage. His power should not be underestimated — ask Hardy.
He is opportunistic, savaging Kim with a flying knee when the opening arose. And he is savvy, sticking to a game plan that emphasized movement and distance against the prickly Diaz in their February fight for the interim title.
Condit (28-5) landed 151 significant strikes to 105 for Diaz, one of the best boxers in MMA. Some 68 of those were kicks directed at Diaz's legs, according to FightMetric which tracks MMA stats.
St-Pierre was cageside that night in Las Vegas, rooting for Diaz to win because the surly California fighter had irked him by not showing up for joint news conferences prior to a previously planned bout.
Irate at Diaz's no-shows, UFC boss Dana White dumped Diaz in favour of Condit-GSP but was eventually forced to match the two contenders when the champion had to withdraw through injury.
St-Pierre insists he had no problem with Condit being given a championship belt of his own that night in February.
"For me the belt doesn't matter. I want to be the best," St-Pierre explained. "It's not really the belt that matters, it's the meaning of it."
Condit will have to deal with St-Pierre's relentless takedowns. According to FightMetric, which tracks MMA stats, St-Pierre tops the UFC with 68 takedowns and a takedown success rate of 77.3 per cent.
"I do feel I'll be able to take him down," said St-Pierre, adding his focus is on what he does and not what Condit can do.
"I want to dictate the pace and make my fight, do what I want to do."
Condit, who has fought less in the UFC than St-Pierre, defends 46 per cent of takedowns according to FightMetric. GSP ranks third in the UFC in takedown defence, stopping 88 per cent of opponents' attempts.
St-Pierre can also use the takedown threat as a decoy, to set up another attack.
St-Pierre's injury-plagued fall in 2011 started with a minor left knee problem and pulled hamstring. Because of the injury, he believes he overcompensated with his right leg when he returned to training.
The result of an attempted takedown during a wrestling drill was a torn anterior cruciate ligament and a small tear to his internal miniscus.
Reconstructive surgery to the right knee followed in mid-December. It was done by Neal ElAttrache, the surgeon who looked after NFL star Tom Brady's knee in 2009.
"My knee feels like it never happened ... It's very strong," St-Pierre said of the surgery which left only "a little scar."
The champion's biggest test is his diet. GSP is something of a foodie. Talk up a restaurant and he will ask you for the address.
"I love eating," he acknowledged.
"No one in my family does sports and they're all muscular and ripped," he added. "They don't have a problem. It's good genetics, I'm lucky. I don't get fat. I'm always in shape."
Since St-Pierre has ties to trainer Greg Jackson and Condit trains at Jackson's MMA in Albuquerque, N.M., the highly regarded coach will sit out the fight.