One of the greatest of all-time might not be done just yet.

Georges St-Pierre told Montreal's Reseau de sports (RDS) last week that the itch to come back to the UFC is coming back in a significant way.

"I'm starting to get the feeling, more and more, to come back," St-Pierre said (translated from French by MMA Fighting). "I watch the fights to see what's going on in my division, and I'm staying in shape. It's like a knife that I have to keep sharp just in case I ever decide to jump back in the mix. It's not for sure that it won't happen in 2015, but I'm not sure yet."

UFC president Dana White has said repeatedly over the last year that he severely doubts St-Pierre will ever return. But GSP, the former UFC welterweight champion, has never used the word retirement and he continues to leave the door open. St-Pierre said he is currently back in the gym at Tristar and working out vigorously.

"I'm training hard," St-Pierre told RDS. "As you can see, I have some bumps and bruises. I didn't get these from falling down stairs."

St-Pierre, 34, successfully defended the title against Johny Hendricks at UFC 167 in November 2013. After the bout, he vaguely alluded to stepping away from MMA for a bit. He elaborated more in the post-fight press conference, and a few weeks later GSP announced he would be relinquishing the title and going on a sabbatical.

Last year, GSP suffered a torn ACL in training, perhaps decreasing the chances of his comeback even more. The Canadian superstar, though, seems to be 100 percent healthy now and maybe even close to fighting shape.

Since his departure, St-Pierre has been extremely vocal about what he feels is a major performance-enhancing drug problem in MMA. He addressed that again last week.

"Many of my regrets in life have nothing to do with things I have done, but rather things I didn't do," GSP said. "And if I have one regret, it's that I didn't speak up sooner. In fact, I've been talking for a while, but they ignored it. At the end, I wanted to make the drug tests public. I should have insisted on that well before."

The UFC has enlisted the U.S. Anti-Doping Agency (USADA) this year to run its drug-testing program. St-Pierre said he has already seen a change since the program went into effect in July.

"I'm not surprised to see certain things," St-Pierre said. "There are fighters whose bodies have changed. They don't look like the same fighters as before. I think a lot of people are scared."

However, GSP does not think the PED epidemic has necessarily been abolished.

"We have to eliminate the technology factor in the sport," St-Pierre said. "The sport needs to be based on talent, technique, athletic talent and not based on who has access to better technology. If I train with a team who supplies me with doctors and biochemists, obviously I am going to have a huge advantage. People have no idea, it makes a big difference. If you take a person and you add force, power, endurance and a new way to recuperate ... it's insane."

St-Pierre's last opponent, Hendricks, ended up in the hospital before what was supposed to be a bout with Tyron Woodley at UFC 192 earlier this month in Houston. Hendricks had a bad weight cut and suffered kidney stones and a dried out intestine.

GSP wishes him well and calls it an "unfortunate situation." He also said steep weight cuts can be a red flag.

"It goes together," St-Pierre said. "Often, big weight cuts rely upon drugs. I'm not accusing anyone, but there are substances used to cut weight and others to recuperate. The science has gone far."