"It is a big day, a massive day for me. I've been looking forward to this day for months," King told BBC Radio Kent.
"All that hard graft in the gym, doing the strengthening work, fitness work and finally I've got the all-clear to give light jogging a go."
The 26-year-old, who was Gillingham's player of the year last season, added: "I'm looking forward to it but am also very scared because I've been out for so long but at the same time I'm also very excited.
"I think the main thing is not to get too disheartened because I have been out for such a long time and it's bound to be a little bit painful tomorrow, and even today the surgeon said it's still going to be a little bit sore.
"Depending on how today goes will depend on how quickly I can get back to fitness and hopefully start training again."
Before Christmas, manager Mark Stimson said he feared his influential defender would miss the entire season, but King is still holding out hope he may get a few games in.
"I'm aiming to definitely to try and get back this season," said King. "Realistically a couple of months from now - maybe late April/start of May for the last couple of games.
"But obviously it depends what situation the club is in.
"If we're in a bit of a dogfight relegation battle then the gaffer might not want to chuck me back in.
"Where as if we've eased away from it and have nothing to play for he might give me a few minutes under my belt, maybe coming off the bench and that will put me in good stead for next year."
Source: BBC Sport
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