Johnson raised the World Championship trophy back in 1986 when he defeated Steve Davis 18-12, going on to lose the final a year later to Davis 18-14.
As a player whose career was cut short by injury, Johnson can emphasize with four-times world champion O'Sullivan, who withdrew from active competition last year thanks in part to battles with depression.
"I'm very excited that he's come back and that he'll open the tournament as defending champion," Johnson told Eurosport-Yahoo!. "It will be great to see Ronnie O'Sullivan back playing snooker again and doing what he does best.
"He says he's come back because he's bored and I can totally believe that. I was forced into retirement because I broke my ankle, so I can understand exactly where he's coming from.
"It's like you've had one of your legs cut off. One minute you've been playing snooker all your life and next you don't have anything to do. There's nothing you can do to replenish the feeling you get from tournament play.
"So although it was Ronnie's own decision to take time off, I can fully understand it when he says he missed competition play because there really is nothing, absolutely nothing, which can take the place of that competitive edge that you've grown used to over your professional career."
Johnson also believes O'Sullivan's decision to return proves that 'The Rocket' will never fully retire from the sport of his own accord.
He explained: "He always threatened in the past to retire and take time out from the game because he was losing passion for the game, and now that he's done that he's found out that he does miss it and that he needs to be playing.
"He may have been bored playing, but he's much more bored not playing!
"You can never be sure what Ronnie will do, but I'm fairly confident from now on he'll play in most events. He's had the time off he needed and will want to get back playing competitively on a regular basis.
"He also has to think about his age, he's 37 now and only got a few years left really at the highest level so he'll also want to make the most of that.
"I think his attitude will be exactly the same, he's always been controversial and I think he always will be, but I do think he's re-found his hunger for the game. He's missed the game and the game has missed him."
The 60-year-old from Bradford is also predicting that O'Sullivan can become a five-time Crucible champion in what would be his most remarkable world title yet.
"I really believe he can win it," Johnson said. "He is the defending champion and the spotlight will be on him, which he loves and thrives on.
"The number two and three seeds are likely to be Judd Trump and Mark Selby and they will also be kept away from him in the other half of the draw.
"He wouldn't have returned without believing he can win it, he has great belief in his own ability.
"Obviously Ronnie's return is bad news for the player who is ranked 16th, as being defending champion he automatically becomes the number one ranked player for the tournament, which means the 16th ranked player moves down to 17th and then has to go through qualification.
"Nowadays qualifying for a tournament is incredibly difficult and a top-16 player can easily lose to a player much lower down the rankings."
The seeding for the 2013 World Championships will be determined by the provisional world rankings after the China Open event, which concludes on March 30.
This year’s World Championships, the traditional season finale, runs from April 20 to May 6 and will be broadcast LIVE on British Eurosport HD, as well as online and on mobile via the .
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